U.S. patent number 5,045,214 [Application Number 07/359,872] was granted by the patent office on 1991-09-03 for methods for removing substances from aqueous solutions.
This patent grant is currently assigned to Union Oil Company of California. Invention is credited to Douglas T. Walker.
United States Patent |
5,045,214 |
Walker |
September 3, 1991 |
**Please see images for:
( Certificate of Correction ) ** |
Methods for removing substances from aqueous solutions
Abstract
Methods are provided for removing contaminants from an aqueous
solution to yield a less contaminated aqueous effluent. In one
embodiment of the invention, the method comprises coprecipitating
non-volatile contaminants (i.e., heavy metals, light metals,
cyanide, phenolics, oil and grease, TSS, BOD, COD, and/or TOC) with
a carrier precipitate which is formed in situ within the aqueous
solution. In another embodiment of the invention, the method
comprises partitioning volatile organic contaminants between a
liquid phase and a gas phase. In yet a further embodiment, the
above versions of the invention are simultaneously performed in the
same reaction vessel.
Inventors: |
Walker; Douglas T. (Elk Grove
Village, IL) |
Assignee: |
Union Oil Company of California
(Los Angeles, CA)
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Family
ID: |
23415642 |
Appl.
No.: |
07/359,872 |
Filed: |
May 31, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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42565 |
Apr 16, 1987 |
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477212 |
Mar 22, 1983 |
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Current U.S.
Class: |
210/717; 210/718;
210/722; 210/724; 210/726; 210/904; 210/908; 210/912; 95/263 |
Current CPC
Class: |
C02F
1/52 (20130101); C02F 1/72 (20130101); C02F
1/5236 (20130101); C02F 2101/18 (20130101); C02F
2101/20 (20130101); C02F 2101/203 (20130101); C02F
2101/22 (20130101); Y10S 210/912 (20130101); Y10S
210/908 (20130101); Y10S 210/904 (20130101) |
Current International
Class: |
C02F
9/00 (20060101); C02F 1/72 (20060101); C02F
1/52 (20060101); C02F 001/20 () |
Field of
Search: |
;75/108,609 ;204/DIG.13
;210/702,708,714,718,721,722,724,726,738,717,750,758,912-914,904,908
;55/53,38 |
References Cited
[Referenced By]
U.S. Patent Documents
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2640096 |
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DE |
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604262 |
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May 1926 |
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FR |
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2210574 |
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Dec 1973 |
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FR |
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2591584 |
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Sep 1985 |
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FR |
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24770 |
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Oct 1968 |
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JP |
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49-11777 |
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Feb 1974 |
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JP |
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51971 |
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May 1975 |
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JP |
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65050 |
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Jun 1975 |
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JP |
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67156 |
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Jun 1977 |
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JP |
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35252 |
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Apr 1978 |
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JP |
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43673 |
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JP |
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67956 |
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JP |
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41270 |
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JP |
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152613 |
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JP |
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84/03692 |
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Sep 1984 |
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WO |
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1142214 |
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Feb 1969 |
|
GB |
|
2035814 |
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Jun 1980 |
|
GB |
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Other References
Merrill et al., Journal Water Pollution Control Federation, 58
(1):18-29 (Jan. 1986). .
Chemical Abstracts, 79 (8):191, Abstract 45500K. .
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Water (Jan. 29, 1988). .
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Employing Unipure Process Technology, Project #0001, (Feb. 2,
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F. Weston, Inc. Lakewood, Colo. (Dec., 1988). .
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Polish Process, Dr. Evord F. Knights (Jun. 28, 1988). .
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1472-1481 (1982). .
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157. .
Takada et al., "Preparation of Ferrites by Wet Method", Proccedings
of the International Conference, Japan, (1970). .
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Oxides and Hydroxides, John Wiley & Sons, Inc., New York, N.Y.
(1935). .
David et al., J. Colloid and Interface Science, 67 (1):90-107
(1978). .
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Dyck, Canadian J. Chemistry, 46:1441-1444 (1968). .
Wilms et al., Advances in Waste Pollution Research, Proceedings of
the Sixth International Conference; Pergamon Press, Oxford, pp.
615-623 (1973). .
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Conference Purdue University, Ann Arbor Science Publications, Ann
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Schwetmann, "Uber die Synthese definierter Eisenoxyde unter
verschiedenen Bedingungen"..
|
Primary Examiner: Hruskoci; Peter
Attorney, Agent or Firm: Wirzbicki; Gregory F. Frieman;
Shlomo R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No.
07/042,565, filed Apr. 16, 1987, which is a continuation of
abandoned application Ser. No. 06/477,212, filed Mar. 22, 1983.
Claims
What is claimed is:
1. A method for removing one or more contaminants selected from the
group consisting of aluminum ions, beryllium ions, and mixtures
thereof from an aqueous solution comprising the contaminants and
ferrous ions, the method comprising the steps of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the contaminants;
and
(b) separating the amorphous precipitate from the solution so as to
form an effluent solution having a substantially reduced
contaminant concentration, wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 30 minutes; step (a) includes the steps of
introducing air into the solution at a rate of about 1 to about 10
l air per about 1,000 ppm ferrous ion present in the solution prior
to step (a), and controlling the pH of the solution so that the pH
of the solution is about 6 to about 9.5; and the total
concentration of the contaminants in the effluent solution is less
than about 10% of the concentration of the contaminants in the
aqueous solution prior to step (a).
2. The method of claim 1 wherein step (a) includes the step of
controlling the pH of the solution with a base selected from the
group consisting of ammonia, hydroxide containing bases, and
mixtures thereof.
3. The method of claim 1 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 15 minutes.
4. The method of claim 1 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 10 minutes.
5. The method of claim 1 wherein step (a) includes the step of
introducing air into the solution at a rate of about 2 to about 8 l
air per about 1000 ppm ferrous ion present in the solution prior to
step (a).
6. The method of claim 1 wherein step (a) includes the step of
mixing the aqueous solution.
7. The method of claim 1 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9.
8. The method of claim 1 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 7.5 to about 8.
9. The method of claim 1 wherein the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
10. The method of claim 1 wherein the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
11. The method of claim 1 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 15 minutes; step (a) includes the steps of
introducing air into the solution at a rate of about 2 to about 8 l
air per about 1000 ppm ferrous ion present in the solution prior to
step (a), and controlling the pH of the solution so that the pH of
the solution is about 6.5 to about 9; and the total concentration
of the contaminants in the effluent solution is less than about 5%
of the concentration of the contaminants in the aqueous solution
prior to step (a).
12. The method of claim 1 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 10 minutes; step (a) includes the steps of
introducing air into the solution at a rate of about 4 to about 10
1 air per about 1000 ppm ferrous ion present in the solution prior
to step (a), and controlling the pH of the solution so that the pH
of
13. The method of claim 1 further comprising the steps of:
(c) introducing additional ferrous ions in the effluent solution to
form a modified effluent solution;
(d) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution; and
(e) separating the second precipitate from the modified effluent
solution so as to form a second effluent solution having a
contaminant concentration less than the contaminant concentration
of the effluent solution.
14. The method of claim 13 wherein step (d) includes the step of
controlling the pH of the modified effluent solution.
15. The method of claim 13 wherein substantially all of the ferrous
ions in the modified effluent solution are oxidized to ferric ions
within a period of less than about 30 minutes.
16. The method of claim 13 wherein step (d) includes the step of
introducing air into the modified effluent solution at a rate of at
least about 1 l air per 1000 ppm ferrous ion present in the
modified effluent solution prior to step (d).
17. The method of claim 13 wherein step (d) includes the step of
introducing air into the modified effluent solution at a rate of at
least about 10 l air 1000 ppm ferrous ion present in the modified
effluent solution prior to step (d).
18. The method of claim 13 wherein step (d) includes the step of
mixing the aqueous solution.
19. The method of claim 13 wherein step (d) includes the step of
controlling the pH of the modified effluent solution so that the pH
of the modified effluent solution is about 6 to about 9.5.
20. The method of claim 1 wherein the method is a continuous
process.
21. The method of claim 1 wherein the method is a batch
process.
22. The method of claim 1 wherein the amorphous precipitate
contains essentially all of the ferric ions formed in step (a).
23. The method of claim 1 wherein the amorphous precipitate
consists essentially of an amorphous material.
24. The method of claim 1 wherein the contaminant is beryllium
ions.
25. A method of removing contaminants selected from the group
consisting of aluminum ions, beryllium ions, cyanide ions, and
mixtures thereof from an aqueous solution comprising the
contaminants and ferrous ions, the method comprising the steps
of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the contaminants;
and
(b) separating the amorphous precipitate from the solution so as to
form an effluent solution having a substantially reduced
contaminant concentration, wherein a portion of the contaminant
concentration, wherein a portion of the contaminants are cyanide
ions and a portion of the contaminants are selected from the group
consisting of aluminum ions, beryllium ions, and mixtures thereof;
the molar ratio of the ferrous ions to the contaminants in the
aqueous solution is about 1:1 to about 10:1; substantially all of
the ferrous ions in the solution are oxidized to ferric ions within
a period of less than about 30 minutes; step (a) includes the steps
of introducing air into the solution at a rate of about 1 to about
10 l air per about 1,000 ppm ferrous ion present in the solution
prior to step (a), and controlling the pH of the solution so that
the pH of the solution is about 6 to about 9.5; the substantially
completely amorphous precipitate comprises a substantial portion of
the cyanide ions; the effluent solution has a substantially reduced
concentration of the cyanide ions; and the total concentration of
the contaminants in the effluent solution is less than about 10% of
the concentration of the contaminants in the aqueous solution prior
to step (a).
26. The method of claim 25 wherein the molar ratio of the ferrous
ions to the contaminants in the aqueous solution is at least about
4:1.
27. The method of claim 25 wherein the molar ratio of the ferrous
ions to the contaminants in the aqueous solution is at least about
8:1.
28. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 1:1.
29. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 4:1.
30. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 8:1.
31. The method of claim 25 wherein the molar ratio of the ferrous
ions to the contaminants in the aqueous solution is about 2:1 to
about 8:1; substantially all of the ferrous ions in the solution
are oxidized to ferric ions within a period of less than about 15
minutes; step (a) includes the steps of introducing air into the
solution at a rate of about 2 to about 8 l air per about 1000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9; and the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
32. The method of claim 25 wherein the molar ratio of the ferrous
ions to the contaminants in the aqueous solution is about 4:1 to
about 8:1; substantially all of the ferrous ions in the solution
are oxidized to ferric ions within a period of less than about 10
minutes; step (a) includes the steps of introducing air into the
solution at a rate of about 4 to about 10 l air per about 1000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 7.5 to about 8; and the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
33. The method of claim 25 wherein a portion of the contaminants
are beryllium ions.
34. The method of claim 25 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 15 minutes.
35. The method of claim 25 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 10 minutes.
36. The method of claim 25 wherein step (a) includes the step of
introducing air into the solution at a rate of about 2 to about 8 l
per about 1000 ppm ferrous ion present in the solution prior to
step (a).
37. The method of claim 25 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9.
38. The method of claim 25 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 7.5 to about 8.
39. The method of claim 25 wherein the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
40. The method of claim 25 wherein the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
41. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 1:1.
42. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 4:1.
43. The method of claim 25 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 8:1.
44. A method for removing contaminants selected the group
consisting of aluminum ions, beryllium ions, heavy metal ions, and
mixtures thereof from an aqueous solution comprising the
contaminants and ferrous ions, the method comprising the steps
of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the contaminants;
and
(b) separating the amorphous precipitate from the solution so as to
form an effluent solution having a substantially reduced
contaminant concentration, wherein a portion of the contaminants
are at least one heavy metal ion and a portion of the contaminants
are selected from the group consisting of aluminum ions, beryllium
ions, and mixtures thereof; the weight ratio of the ferrous ions to
the contaminants in the aqueous solution is at least about 1:1;
substantially all of the ferrous ions in the solution are oxidized
to ferric ions within a period of less than about 30 minutes; step
(a) includes the steps of introducing air into the solution at a
rate of about 1 to about 10 l air per about 1000 ppm ferrous ion
present in the solution prior to step (a), and controlling the pH
of the solution so that the pH of the solution is about 6 to about
9.5: the substantially completely amorphous precipitate comprises a
substantial portion of the heavy metal ions; the effluent solution
has a substantially reduced concentration of the heavy metal ions;
and the total concentration of the contaminants in the effluent
solution is less than about 10% of the concentration of the
contaminants in the aqueous solution prior to step (a).
45. The method of claim 44 wherein the weight ratio of the ferrous
ions to the contaminants in the aqueous solution is less than about
10:1.
46. The method of claim 44 wherein the weight ratio of the ferrous
ions to the contaminants in the aqueous solution is about 1:1 to
about 10:1.
47. The method of claim 44 wherein the weight ratio of the ferrous
ions to the contaminants in the aqueous solution is about 4:1 to
about 6:1.
48. The method of claim 44 wherein the weight ratio of the ferrous
ions to the contaminants in the aqueous solution is about 1:1 to
about 10:1; substantially all of the ferrous ions in the solution
are oxidized to ferric ions within a period of less than about 15
minutes; step (a) includes the steps of introducing air into the
solution at a rate of about 2 to about 8 l air per about 1000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9; and the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
49. The method of claim 44 wherein the weight ratio of the ferrous
ions to the contaminants in the aqueous solution is about 4:1 to
about 6:1; substantially all of the ferrous ions in the solution
are oxidized to ferric ions within a period of less than about 10
minutes; step (a) includes the steps of introducing air into the
solution at a rate of about 4 to about 10 l air per about 1000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 7.5 to about 8; and the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
50. The method of claim 44 wherein the contaminants further
comprise step (a) includes the step of occluding a substantial
portion of the heavy metal contaminant in the amorphous
precipitate.
51. The method of claim 44 wherein a portion of the contaminants
are beryllium ions.
52. The method of claim 44 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 15 minutes.
53. The method of claim 44 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 10 minutes.
54. The method of claim 44 wherein step (a) includes the step of
introducing air into the solution at a rate of about 2 to about 8 l
per about 1000 ppm ferrous ion present in the solution prior to
step (a).
55. The method of claim 44 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9.
56. The method of claim 44 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 7.5 to about 8.
57. The method of claim 44 wherein the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
58. The method of claim 44 wherein the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
59. The method of claim 44 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 1:1.
60. The method of claim 44 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 4:1.
61. The method of claim 44 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 8:1.
62. A method for removing contaminants selected from the group
consisting of aluminum ions, beryllium ions, cyanide ions, heavy
metal ions, and mixtures thereof from an aqueous solution
comprising the contaminants and ferrous ions, the method comprising
the steps of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the contaminants;
and
(b) separating the amorphous precipitate from the solution so as to
form an effluent solution having a substantially reduced
contaminant concentration, wherein a portion of the contaminants
are cyanide ions and at least one heavy metal ion and a portion of
the contaminants are selected from the group consisting of aluminum
ions, beryllium ions, and mixtures thereof; the substantially
completely amorphous precipitate comprises a substantial portion of
the cyanide ions and the heavy metal ions; the effluent solution
has a substantially reduced concentration of the cyanide ions and
the heavy metal ions; the concentration of the ferrous ions in the
aqueous solution is equal to about one to about ten times the molar
concentration of the contaminants; substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 30 minutes; step (a) includes the steps of
introducing air into the solution at a rate of about 1 to about 10
l air per about 1,000 ppm ferrous ion present in the solution prior
to step (a), and controlling the pH of the solution so that the pH
of the solution is about 6 to about 9.5; and the total
concentration of the contaminants in the effluent solution is less
than about 10% of the concentration of the contaminants in the
aqueous solution prior to step (a).
63. The method of claim 62 wherein the concentration of the ferrous
ions in the aqueous solution is equal to about two to about eight
times the molar concentration of the contaminants.
64. The method of claim 62 wherein the concentration of the ferrous
ions in the aqueous solution is equal to about four to about six
times the molar concentration of the contaminants.
65. The method of claim 62 wherein the concentration of the ferrous
ions in the aqueous solution is equal to about two to about eight
times the molar concentration of the contaminants; substantially
all of the ferrous ions in the solution are oxidized to ferric ions
within a period of less than about 15 minutes; step (a) includes
the steps of introducing air into the solution at a rate of about 2
to about 8 l air per about 1000 ppm ferrous ion present in the
solution prior to step (a), and controlling the pH of the solution
so that the pH of the solution is about 6.5 to about 9; and the
total concentration of the contaminants in the effluent solution is
less than about 5% of the concentration of the contaminants in the
aqueous solution prior to step (a).
66. The method of claim 62 wherein the concentration of the ferrous
ions in the aqueous solution is equal to about four to about six
times the molar concentration of the contaminants; substantially
all of the ferrous ions in the solution are oxidized to ferric ions
within a period of less than about 10 minutes; step (a) includes
the steps of introducing air into the solution at a rate of about 4
to about 10 l air per about 1000 ppm ferrous ion present in the
solution prior to step (a), and controlling the pH of the solution
so that the pH of the solution is about 7.5 to about 8; and the
total concentration of the contaminants in the effluent solution is
less than about 1% of the concentration of the contaminants in the
aqueous solution prior to step (a).
67. The method of claim 62 wherein a portion of the contaminants
are beryllium ions.
68. The method of claim 62 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 15 minutes.
69. The method of claim 62 wherein substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 10 minutes.
70. The method of claim 62 wherein step (a) includes the step of
introducing air into the solution at a rate of about 2 to about 8 l
per about 1000 pm ferrous ion present in the solution prior to step
(a).
71. The method of claim 62 wherein step (a) includes the step of
controlling the pH of the solution so that the pH of the solution
is about 6.5 to about 9.
72. The method of claim 62 wherein step (a) includes the step of
controlling the pH of the solution so That the pH of the solution
is about 7.5 to about 8.
73. The method of claim 62 wherein the total concentration of the
contaminants in the effluent solution is less than about 5% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
74. The method of claim 62 wherein the total concentration of the
contaminants in the effluent solution is less than about 1% of the
concentration of the contaminants in the aqueous solution prior to
step (a).
75. The method of claim 62 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 1:1.
76. The method of claim 62 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 4:1.
77. The method of claim 62 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 8:1.
78. A method for removing volatile organics and one or more
contaminants selected from the group consisting of aluminum ions,
beryllium ions, and mixtures thereof from an aqueous solution
comprising the volatile organics, the contaminants, and ferrous
ions, the method comprising the steps of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the
contaminants;
(b) removing a substantial portion of the volatile organics by
introducing a gas into the solution at a rate sufficient to achieve
an average volumetric flux ratio of gas to water of at least about
20; and
(c) separating the precipitate from the solution so as to form an
effluent solution having a reduced contaminant and volatile organic
concentration, wherein steps (a) and (b) are performed
simultaneously and include the steps of introducing air into the
solution at a rate of about 1 to about 10 l air per about 1,000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 6 to about 9.5; substantially all of the ferrous ions in
the solution are oxidized to ferric ions within a period of less
than about 30 minutes; and the total concentration of the
contaminants in the effluent solution is less than about 10% of the
concentration of the contaminants in the aqueous solution prior to
step (a), and the concentration of the volatile organics in the
effluent is less than about 20% of the concentration of the
volatile organics in the aqueous solution prior to step (b).
79. The method of claim 78 wherein steps (a) and (b) include the
step of mixing the aqueous solution.
80. The method of claim 78 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution; and
(f) separating the second precipitate from the modified effluent
solution so as to form a second effluent solution having a
contaminant concentration less than the contaminant concentration
of the effluent solution.
81. The method of claim 78 further comprising the steps of
introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20 so that any volatile organic content to
the effluent is further reduced.
82. The method of claim 78 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution;
(f) introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20; and
(g) separating the precipitate from the modified effluent solution
so as to form a second effluent solution having a contaminant and
volatile organic concentration less than the contaminant volatile
organic concentration of the effluent solution.
83. The method of claim 78 wherein the contaminant is beryllium
ions.
84. A method for removing volatile organics and contaminants
selected from the group consisting of aluminum ions, beryllium
ions, cyanide ions, and mixtures thereof from an aqueous solution
comprising the volatile organics, the contaminants, and ferrous
ions, the method comprising the steps of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the
contaminants;
(b) removing a substantial portion of the volatile organics by
introducing a gas into the solution at a rate sufficient to achieve
an average volumetric flux ratio of gas to water of at least about
20; and
(c) separating the precipitate from the solution so as to form an
effluent solution having a reduced contaminant and volatile organic
concentration, wherein a portion of the contaminants are cyanide
ions and a portion of the contaminants are selected from the group
consisting of aluminum ions, beryllium ions, and mixtures thereof;
the molar ratio of the ferrous ions to the contaminants in the
aqueous solution is about 1:1 to about 10:1; substantially all of
the ferrous ions in the solution are oxidized to ferric ions within
a period of less than about 30 minutes; steps (a) and (b) are
performed simultaneously and include the steps of introducing air
into the solution at a rate of about 1 to about 10 l air per about
1,000 ppm ferrous ion present in the solution prior to step (a),
and controlling the pH of the solution so that the pH of the
solution is about 6 to about 9.5; the substantially completely
amorphous precipitate comprises a substantial portion of the
cyanide ions; the effluent solution has a substantially reduced
concentration of the cyanide ions; and the total concentration of
the contaminants in the effluent solution is less than about 10% of
the concentration of the contaminants in the aqueous solution prior
to step (a), and the concentration of the volatile organics in the
effluent is less than about 20% of the concentration of the
volatile organics in the aqueous solution prior to step (b).
85. The method of claim 84 further comprising the step of adding
ferrous ions to the aqueous solution to increase the ferrous
ion-contaminant molar ratio to at least about 1:1.
86. The method of claim 84 wherein a portion of the contaminants
are beryllium ions.
87. The method of claim 84 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution; and
(f) separating the second precipitate from the modified effluent
solution so as to form a second effluent solution having a
contaminant concentration less than the contaminant concentration
of the effluent solution.
88. The method of claim 84 further comprising the steps of
introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20 so that any volatile organic content to
the effluent is further reduced.
89. The method of claim 84 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution;
(f) introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20; and
(g) separating the precipitates from the modified effluent solution
so as to form a second effluent solution having a contaminant and
volatile organic concentration less than the contaminant and
volatile organic concentration of the effluent solution.
90. A method for removing volatile organics and contaminants
selected from the group consisting of aluminum ions, beryllium
ions, heavy metal ions, and mixtures thereof from an aqueous
solution comprising the volatile organics, the contaminants, and
ferrous ions, the method comprising the steps of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the
contaminants;
(b) removing a substantial portion of the volatile organics by
introducing a gas into the solution at a rate sufficient to achieve
an average volumetric flux ratio of gas to water of at least about
20; and
(c) separating the precipitate from the solution so as to form an
effluent solution having a reduced contaminant and volatile organic
concentration, wherein a portion of the contaminants are at least
one heavy metal ion and a portion of the contaminants are selected
from the group consisting of aluminum ions, beryllium ions, and
mixtures thereof; the molar ratio of the ferrous ions to the
contaminants in the aqueous solution is at least about 1:1;
substantially all of the ferrous ions in the solution are oxidized
to ferric ions within a period of less than about 30 minutes; steps
(a) and (b) are performed simultaneously and include the steps of
introducing air into the solution at a rate of about 1 to about 10
l air per about 1,000 ppm ferrous ion present in the solution prior
to step (a), and controlling the pH of the solution so that the pH
of the solution is about 6 to about 9.5; the substantially
completely amorphous precipitate comprises a substantial portion of
the heavy metal ions; the effluent solution has a substantially
reduced concentration of the heavy metal ions; and the total
concentration of the contaminants in the effluent solution is less
than about 10% of the concentration of the contaminants in the
aqueous solution prior to step (a), and the concentration of the
volatile organics in the effluent is less than about 20% of the
concentration of the volatile organics in the aqueous solution
prior to step (b).
91. The method of claim 90 wherein a portion of the contaminants
are beryllium ions.
92. The method of claim 90 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution; and
(f) separating the second precipitate from the modified effluent
solution so as to form a second effluent solution having a
contaminant concentration less than the contaminant concentration
of the effluent solution.
93. The method of claim 90 further comprising the steps of
introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20 so that any volatile organic content to
the effluent is further reduced.
94. The method of claim 90 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution;
(f) introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20; and
(g) separating the precipitates from the modified effluent solution
so as to form a second effluent solution having a contaminant and
volatile organic concentration less than the contaminant and
volatile organic concentration of the effluent solution.
95. A method for removing volatile organics and contaminants
selected from the group consisting of aluminum ions, beryllium
ions, cyanide ions, heavy metal ions, and mixtures thereof from an
aqueous solution comprising the volatile organics, the
contaminants, and ferrous ions, the method comprising the steps
of:
(a) rapidly oxidizing substantially all the ferrous ions in the
solution to ferric ions so as to rapidly form a substantially
completely amorphous precipitate comprising a substantial portion
of ferric hydroxide and a substantial portion of the
contaminants;
(b) removing a substantial portion of the volatile organics by
introducing a gas into the solution at a rate sufficient to achieve
an average volumetric flux ratio of gas to water of at least about
20; and
(c) separating the precipitate from the solution so as to form an
effluent solution having a reduced contaminant and volatile organic
concentration, wherein a portion of the contaminants are cyanide
ions and at least one heavy metal ion and a portion of the
contaminants are selected from the group consisting of aluminum
ions, beryllium ions, and mixtures thereof; the substantially
completely amorphous precipitate comprises a substantial portion of
the cyanide ions and the heavy metal ions; the effluent solution
has a substantially reduced concentration of the cyanide ions and
the heavy metal ions; the concentration of the ferrous ions in the
aqueous solution is equal to about one to abut ten times the molar
concentration of the contaminants; substantially all of the ferrous
ions in the solution are oxidized to ferric ions within a period of
less than about 30 minutes; steps (a) and (b) are performed
simultaneously and include the steps of introducing air into the
solution at a rate of about 1 to about 10 l air per about 1,000 ppm
ferrous ion present in the solution prior to step (a), and
controlling the pH of the solution so that the pH of the solution
is about 6 to about 9.5; and the total concentration of the
contaminants in the effluent solution is less than about 10% of the
concentration of the contaminants in the aqueous solution prior to
step (a), and the concentration of the volatile organics in the
effluent is less than about 20% of the concentration of the
volatile organics in the aqueous solution prior to step (b).
96. The method of claim 95 wherein a portion of the contaminants
are beryllium ions.
97. The method of claim 95 further comprising the steps of:
(d) introducing additional ferrous ions into the effluent solution
to form a modified effluent solution;
(e) rapidly oxidizing substantially all the ferrous ions in the
modified effluent solution to ferric ions so as to rapidly form a
second substantially completely amorphous precipitate comprising a
substantial portion of ferric hydroxide and a substantial portion
of any contaminant present in the effluent solution; and
(f) separating the second precipitate from the modified effluent
solution so as to form a second effluent solution having a
contaminant concentration less than the contaminant concentration
of the effluent solution.
98. The method of claim 95 further comprising the steps of
introducing additional gas into the effluent solution at a rate
sufficient to achieve an average volumetric flux ratio of gas to
water of at least about 20 so that any volatile organic content to
the effluent is further reduced.
Description
BACKGROUND OF THE INVENTION
One aspect of this invention relates generally to the removal of
heavy metals from aqueous solutions and, in particular, to the
removal of heavy metals from aqueous solutions by the method of
coprecipitation. As used herein, the term "heavy metals" refers to
non-ferrous metals and metaloids (e.g., arsenic, selenium, and
antimony) which have an atomic number greater than that of
calcium.
There is increasing concern over the hazards posed by the rising
levels of heavy metals within the world's water supplies. Most
heavy metals are toxic to some degree to all life-forms. Aqueous
concentrations of as little as 0.05 ppm can have a deleterious
effect on aquatic flora and fauna. In humans, toxic heavy metal
poisoning can lead to severe nervous system disorders and can cause
death. Even trace amounts of heavy metals within an organism's
environment are potentially dangerous, because heavy metals do not
decompose over time (as do most organic pollutants) and often
accumulate within the organism throughout its lifetime. This
accumulative effect is accentuated in succeeding species along each
food chain.
As a consequence of the increasing concern over aqueous heavy metal
concentration levels, industry is being required to virtually
eliminate heavy metals from its aqueous wastes. For many
industries, however, this requirement is very difficult to fulfill.
The metal finishing industries, for example, employ a variety of
processes which generate large volumes of aqueous waste material.
Many of these wastes contain high concentrations of heavy metals
(often as high as 10 percent), including zinc, nickel, copper,
chromium, lead, cadmium, tin, gold, and silver. The combined
quantity of these wastes generated daily is very large (over one
billion gallons in the United States), and the number of plants
employing metal finishing processes is also large (nearly 8,000 in
the United States). Numerous heavy metal removal methods have been
proposed for the metal finishing industries, including dilution,
evaporation, alkali-precipitation, absorption, dialysis,
electrodialysis, reverse osmosis, and ion exchange, but none has
been found to be entirely satisfactory.
By far the most common heavy metal removal method is
alkali-precipitation. In this method, a sufficient quantity of base
is added to the aqueous waste solution to precipitate the desired
quantity of heavy metals as insoluble metal hydroxides. However, as
governmental heavy metal regulations have become stricter, the
alkali precipitation method has become exceedingly costly, more
difficult to use, and in some instances inappropriate.
Alkali-precipitation must be carried out at high pH (between about
9 and about 12) in order to reduce the soluble heavy metal
concentrations to within acceptable limits. Additive chemical
volumes can therefore be quite high. Large quantities of base are
required to raise the waste solution pH to treatment conditions and
to precipitate the requisite quantity of heavy metals. Large
quantities of acid are often required to reduce the pH of the
resulting treated effluent prior to its recycle or disposal.
Additive chemical unit costs are also quite high because a costly
base, such as caustic soda, must be employed. The most preferable
base, aqueous ammonia (because it is less expensive and easier to
handle than caustic soda), is impractical in the
alkali-precipitation method. At the high solution pH levels
required by the alkali-precipitation method, aqueous ammonia forms
soluble complexes with many heavy metal species (especially with
copper, nickel, and zinc) thereby preventing their
precipitation.
Waste streams containing hexavalent chromium, a common contaminant
in many metal finishing industry waste solutions, require costly
pretreatment because the alkali-precipitation method is ineffective
in precipitating hexavalent chromium. The pretreatment step entails
reducing the hexavalent chromium to the trivalent state by reaction
with a suitable reducing agent, such as sodium bisulfite, at pH
levels below 3. After pretreatment, the trivalent chromium is
precipitated from the solution as a hydroxide by raising the
solution pH to above about 9.
Waste streams containing organic and nitrogenous complexing agents,
also common contaminants in many metal finishing industry waste
solutions, require a specialized and especially costly
alkali-precipitation treatment. To counter the tendency of the
complexing agents to solubilize heavy metals, large quantities of
calcium hydroxide must be added to the waste solution. The large
quantities of base necessarily raise the pH of the solution to very
high levels, and make necessary the eventual use of large
quantities of acid to neutralize the resulting effluent. The
necessary use of calcium hydroxide also results in significantly
increased operating costs because calcium hydroxide exists as a
slurry at treatment conditions and is, therefore, very difficult to
handle and control. Furthermore, having to use calcium hydroxide in
such high concentrations results in large precipitate sludge
disposal costs because abnormally large volumes of sludge are
produced. This abnormal sludge production stems from (a) the fact
that, in addition to the formation of heavy metal precipitates,
calcium precipitates are formed as well, and (b) the fact that
calcium precipitates tend to retain a large amount of water.
Various light metals, e.g., beryllium and aluminum, are also
undesirable contaminants. Prior art methods for removing light
metals from aqueous systems are not satisfactory. For example,
although aluminum can be removed by alkaline precipitation, the
resulting flocculent or precipitate (aluminum tetrahydroxide) is
very hygroscopic and is difficult to settle. In addition, alkaline
precipitation is ineffective in treating concentrated aluminum
solutions. Furthermore, aluminum readily redissolves out of the
precipitate.
With respect to beryllium, beryllium is a small, hydrated,
unreactive atom that is generally only removal from a solution by
methods capable of removing sodium, e.g., ion chromatography.
Cyanide is also a hazardous contaminant. Although prior art methods
for reducing the cyanide concentration in aqueous systems exist,
these methods generally require that the cyanide be treated
separately. Accordingly, if other contaminants are present in a
cyanide-containing solution, a multi-step process is required to
remove all the contaminants. The use of separate steps to remove
the cyanide and other contaminants increases the cost of the
treatment process.
In addition, governmental regulations restrict the amount of
organic contaminants that can be present in water. Exemplary
organic contaminants include volatile organics, phenolics, oil and
grease, and organic contaminants measured in terms of total
suspended solids (TSS), biological oxygen demand (BOD), chemical
oxygen demand (COD), and total organic carbon (TOC). Unfortunately,
compliance with these governmental regulations is not always
possible because it is difficult to remove sufficient organic
contaminants with prior art organic contaminant removal
methods.
SUMMARY OF THE INVENTION
In accordance with the present invention, methods are provided for
removing contaminants from an aqueous solution. In one version, the
method comprises coprecipitating heavy metal ions with a carrier
precipitate which is formed in situ within the aqueous solution. In
another version, the method comprises coprecipitating light metal
ions with a carrier precipitate which is formed in situ within the
aqueous solution. In a third version, the method entails
coprecipitating cyanide ions with a carrier precipitate which is
formed in situ within the aqueous solution. If a mixture of heavy
metal ions, light metal ions, and/or cyanide ions are present in
the aqueous solution, these contaminants can be simultaneously
coprecipitated using the same methodology.
Use of the above methods results in reducing the presence of heavy
metal ions, light metal ions, and cyanide ions in the aqueous
solution to below their thermodynamic equilibrium concentrations.
This extraordinary result affords the user the unique ability to
substantially reduce high aqueous concentrations of heavy and light
metals as well as cyanide often to within legally acceptable
concentrations, while maintaining the aqueous solution at near
neutral pH.
In addition, methods are also provided for removing volatile
organics, phenolics, oil and grease, TSS contributors, BOD
contributors, COD contributors, and TOC contributors from an
aqueous solution. The phenolics, oil and grease, TSS contributors,
BOD contributors, and/or TOC contributors present in an aqueous
solution are removed by adsorption onto a carrier precipitate which
is formed in situ within the aqueous solution. The carrier
precipitate preferably is the same precipitate used to remove the
heavy metals, the light metals, and/or cyanide.
In each of the above embodiments of the invention, the preferred
method involves rapidly forming the precipitate at a controlled pH
by quickly oxidizing ferrous ions to form a substantially
completely amorphous ferric hydroxide-containing precipitate that
also contains a major portion of the non-volatile contaminants
originally present in the aqueous solution.
With respect to the volatile organics, these are removed by
sparging air through the aqueous solution. In addition, the
volatile organic removal process and above discussed precipitation
process can be performed simultaneously in the same vessel.
Accordingly, the (a) phenolics, oil and grease, TSS contributors,
BOD contributors, and/or TOC contributors, (b) heavy metal ions,
light metal ions, and/or cyanide ions, and/or (c) volatile organics
can be simultaneously removed from the same aqueous solution in the
same reaction vessel.
BRIEF DESCRIPTION OF THE DRAWING
The present invention will be more readily understood by reference
to the drawing which schematically illustrates a waste water
treatment system embodying features of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The method of the invention can be used to remove the following
contaminants from nearly any aqueous stream: dissolved heavy
metals, light metals, TSS contributors, BOD contributors, COD
contributors, TOC contributors, volatile organics, and/or iron. The
invention will now be described first with respect to heavy metals,
then light metals and cyanide, next phenolics, oil and grease, TSS
contributors, BOD contributors, COD contributors, and TOC
contributors, and finally with respect to volatile organics. Unless
otherwise stated, all process and apparatus parameters disclosed
for heavy metal removal are equally effective for the removal of
the other contaminants as well. Likewise, unless otherwise stated,
all process and apparatus parameters disclosed for the removal of
the other non-volatile contaminants are equally effective for heavy
metal removal as well.
With respect to heavy metals, the invention is particularly useful
in removing the large concentrations of copper, nickel, zinc, gold,
silver, cadmium, tin, chromium, lead, vanadium, mercury, titanium,
selenium, antimony, and molybdenum from pickling acid wastes and
other acidic waste streams formed in the metal finishing
industries. In the method of the invention, an amorphous carrier
precipitate is created within an aqueous waste solution which is
contaminated with heavy metals and/or iron. The contaminants are
thereby caused to coprecipitate with the carrier precipitate and
are thus removed from the aqueous solution.
"Coprecipitation" as used with respect to the invention described
herein refers to the chemical phenomenon where, within an aqueous
solution containing a cationic carrier precipitate precursor, an
anionic carrier precipitate precursor, and one or more
coprecipitant precursors, the cationic and anionic carrier
precipitate precursors are caused to chemically react and
precipitate out of the aqueous solution as carrier precipitate
particles; and, as the carrier precipitate particles are formed,
coprecipitant precursors are removed from the aqueous solution by
adsorption onto the surface of the carrier precipitate particle
and/or by occlusion within the interior of the carrier precipitate
particle. The term "occlusion" as used herein refers to the
entrapment of foreign ions within a precipitate particle by
physical encapsulation within the particle walls and by chemical
bonding within the particle structure.
It has been discovered that by the method of the invention a heavy
metal-rich aqueous solution can be transformed into a liquid solid
mixture wherein the liquid-phase heavy metal concentrations are
substantially lower than their respective equilibrium
concentrations. Although the invention is not limited to any
particular theory of operation, the reduction of heavy metal
concentrations below their equilibrium concentrations is believed
to result, in part, from the large quantities of heavy metals which
are occluded within the amorphous carrier precipitate structure.
The proportion of the dissolved heavy metals which become occluded
is typically greater than 10 weight percent, frequently greater
than 50 weight percent and often greater than 80 weight percent. By
segregating the liquid-phase of the mixture from the amorphous
solid-phase, a stable aqueous effluent is produced which is
substantially free of heavy metals. It has been further discovered
that the method of the invention results in liquid-phase heavy
metal concentrations which are so much lower than their respective
equilibrium values that environmentally innocuous liquid effluents
can be produced from heavy metal concentrated solutions, even when
the liquid phases are maintained at near neutral pH.
In the embodiment of the invention illustrated in the drawing, an
acid waste stream containing heavy metal ions in concentrations
usually above 50 ppmw, typically greater than 100 ppmw, frequently
greater than 1,000 ppmw and often greater than 10,000 ppmw is
generated in an industrial process 6. This stream is transferred
from the industrial process 6 via a conduit 8. Carrier precipitate
precursor cations from a source 10 are added to the stream via a
conduit 12 to raise the concentration of such cations sufficiently
so that the molar ratio of such cations to heavy metal ions within
the stream is preferably greater than 1:1, more preferably greater
than 4:1, and most preferably greater than 8:1. However, the molar
ratio of carrier precipitate precursor cations to heavy metal ions
is typically less than about 10:1. In a preferred embodiment of the
invention, wherein the carrier precipitate is amorphous oxyferric
hydroxide (hereinafter referred to as "ferric hydroxide"), ferrous
ions are preferably added as the carrier precipitate precursor
cations to achieve the desired molar ratio of ferrous ions to heavy
metal ions. However, since waste streams rich in heavy metals are
commonly rich in dissolved iron as well, sometimes only little or
no addition of ferrous ions from the source 10 is necessary.
Carrier precipitate precursor anions are also added to the waste
acid stream. Preferably, such anions are added in sufficient
quantities to raise the concentration of such anions within the
waste stream to above the stoichiometric concentration necessary to
react with all solubilized carrier precipitate precursor cations,
and more preferably above 110 percent of such stoichiometric
concentration. The addition of such anions can be made by injection
into the conduit 8 (not shown) or by addition to vessels 14 and 16
(as described hereinafter). In the embodiment shown in the drawing,
addition of the anions is made in two stages to allow for accurate
pH control. This two stage pH control is especially preferred for
use when ammonia is the selected base and complexable metal cations
are present in the waste water. Accordingly, as illustrated in the
drawing, the waste acid stream from the industrial process 6 is
transferred via the conduit 8 to the mixing vessel 14. The anions
are added as part of a base from a source 18 to the acid waste
solution within the vessel 14 via a conduit 20. Exemplary bases
include aqueous ammonia, hydroxide containing bases (e.g., sodium
hydroxide, calcium hydroxide, potassium hydroxide, magnesium
hydroxide, etc.), and mixtures thereof.
Rapid mixing of the solution within the vessel 14 is preferably
assured by the use of a mixing device 22. Sufficient base is added
to the solution within the vessel 14 to raise the solution pH to
between about 5.5 and about 6.5. The partially neutralized waste
solution is then transferred, via a conduit 24, to the
precipitation vessel 16. Via a conduit 26, additional base from the
source 18 is added to the waste solution within the vessel 16 in
sufficient quantities to raise the solution pH to between about 6.5
and about 9.5, preferably to between about 6.5 and about 9, e.g.,
about 6.5 to about 8 or about 6.5 to about 7.5, but most preferably
to between about 7.5 to about 8.
Within the vessel 16, the carrier precipitate precursor cations are
caused to react with the carrier precipitate precursor anions and
precipitate out of solution. As the amorphous carrier precipitate
forms, substantial quantities of heavy metal ions coprecipitate
with the carrier precipitate and are thereby removed from the
solution. In the preferred embodiment wherein the carrier
precipitate is ferric hydroxide, precipitation is triggered by the
oxidation of ferrous ions to ferric ions. Accordingly, as
illustrated in the drawing, an oxidizing agent, e.g., air, oxygen,
and mixtures thereof, from a source 28, is added to the acid waste
stream via a conduit 30. The preferred oxidizing agent is air.
Sufficient oxidizing agent is added to rapidly oxidize essentially
all of the dissolved ferrous ions to ferric ions. When air is the
selected oxidizing agent, the rate of air addition is preferably
sufficient to oxidize all of the ferrous ions and to air-saturate
the solution.
A dispersion device 32 and/or a mixing device 34 can be used to
assure rapid and thorough mixing of the waste solution, additive
base, and additive oxidant within the vessel 16. The function of
the mixing device 34 is, in part, to shear or otherwise reduce the
size of the bubbles that emerge from the dispersion device 32. An
exemplary dispersion device 32 is a multi-perforated tube. In
general, the cross-sectional area of the multi-perforated tube is
selected so that the air flow rate divided by the cross-sectional
area is from about 50 to about 150 ft/sec. The remaining dimensions
of the multi-perforated pipe are selected in accordance with the
rule of thumb for design of perforated-pipe distributors as
discussed in Perry's Chemical Engineers' Handbook, Perry et al.
Editors, 4th ed., McGraw-Hill Book Company, New York, N.Y. (1963),
page 5-45, the publication being incorporated herein by
reference.
The coprecipitant reaction is very rapid. Typically, more than 95
weight percent, and usually more than 99 weight percent, of the
heavy metals are removed from the waste solution within about 8
minutes after the formation of the first 5 weight percent of the
carrier precipitate. After this 8 minute period, the remaining
solubilized heavy metals generally continue to be adsorbed onto the
precipitate particles. The ideal residence time of the aqueous
solution within the vessel 16 and a separator 36 (described
hereinafter) varies with each particular operation situation, and
the optimizing of such residence time will, in each situation,
require some routine adjustment.
From the vessel 16, aqueous effluent, now substantially reduced in
dissolved heavy metal content, is transferred together with the
nascent precipitate to the solids separator device 36 via a conduit
38. The precipitate is essentially completely amorphous. Within the
separator 36 the effluent and amorphous precipitate are segregated
into two streams. The separator 36 is comprised of a clarifier,
filter, centrifuge, settling pond or other suitable liquid-solid
separating equipment capable of segregating the precipitate
particles from the aqueous effluent. The segregated precipitate is
removed from the separator 36 as a sludge and is transferred to a
suitable disposal site (not shown) via a conduit 40.
Although in some embodiments of the invention it is desirable to
return a portion of the sludge to either the mixing vessel 14 or
the precipitation vessel 16 via a conduit (not shown), in the
preferred version of the invention none of the sludge is returned
to any portion of the treatment system. In fact, it is most
preferred that no water insoluble matter be added to the mixing
vessel 14 or the precipitation vessel 16 or any portion of the
system feeding into either of these vessels 14 or 16. However, some
bases suitable for use in the present invention may be only
partially water soluble. These partially water soluble bases can be
employed in the most preferred embodiment of the present invention
provided that they are substantially devoid of iron-containing,
water-insoluble compounds.
The corresponding aqueous effluent, which typically contains less
than 15 ppmw heavy metals and usually contains less than 5 ppm
heavy metals, can be recycled to the industrial process 6 via a
conduit 42. In those cases where it is desired that the recycled
effluent be less basic than the solution within the separator 36
(e.g., where the recycled effluent is to be used as an acid makeup
solution), acid from a source 44 is added to the recycled effluent
via a conduit 46. Optionally, the treated effluent from the
separator 36 is discharged to a disposal site (not shown) via a
conduit 48. Preferably, the concentrations of heavy metals within
the treated effluent are reduced to below the relevant legal limits
so that non-recycled effluent can be discharged directly to a
municipal sewer.
Although the preceding description of one embodiment of the
invention assumes that the aqueous waste solution is an acid waste,
the invention is not limited to the treatment of such wastes.
Furthermore, although the preceding description of the invention
describes a continuous process, the invention can also be practiced
as a batch process. In addition, although the carrier precipitate
precursor cations (e.g., ferrous ions) have been shown to be
originally present in the acid waste stream or added to the acid
waste stream via the conduit 8, in an alternative embodiment of the
invention the cations are added directly to the precipitation
vessel 16 or to any liquid flowing into the precipitation vessel
16. Also, although the pretreatment vessel 14 is shown in the
drawing, it is more preferred to introduce the waste stream
directly into the precipitation vessel 16 along with the required
base, and thus avoid the need for the pretreatment vessel 14.
Generally, the pretreatment vessel 14 is used when ammonia is the
desired base and the waste water contains complexable metal
cations, but even in these situations it is not critical that the
two stage pH control be used.
Preferably, the choices of carrier precipitate precursors and
operating conditions are made so as to maximize the removal of
heavy metal ions while minimizing treatment costs. Towards that end
the choices are generally made so as to (1) produce a carrier
precipitate structure which is conducive to heavy metal occlusion,
(2) produce a carrier precipitate particle surface which is
conducive to adsorption, (3) form the carrier precipitate as
rapidly as possible, and (4) minimize extraneous reactions which
interfere with heavy metal coprecipitation.
The carrier precipitate cation and anion are generally chosen so
that, when the carrier precipitate is forming, the developing
precipitate is conducive to the occlusion of heavy metals. The
carrier precipitate cations of choice are those which have
approximately the same ionic diameter as most of the contaminant
heavy metals. The similarity of ionic diameter makes it conducive
for the forming carrier precipitate to accept heavy metal ions in
substitution for carrier precipitate cations. When substituted
heavy metal ions are similar in size to the cations, the
precipitate structure is not unduly stressed by the heavy metal
inclusion. Thus, preferably, the ionic diameter of the carrier
precipitate precursor cation is between about 75 percent and about
125 percent of the ionic diameter of the most common heavy metal
contaminant within the waste solution.
The preferred carrier precipitate cations are metal ions, with the
ions of aluminum, calcium, iron (ferrous), and magnesium being more
preferred. Most preferred are iron ions, because such ions closely
approximate the size of most contaminant heavy metals and because
it is common for large natural concentrations of iron ions to be
dissolved within heavy metal-rich waste streams.
The carrier precipitate anions of choice are those which form
insoluble salts with the contaminant heavy metals as well as with
the carrier precipitate cations. Such anions have a strong
attraction for heavy metal ions, and the degree of heavy metal
occlusion is directly proportional to the strength of the
anion-heavy metal bonds. This proportionality stems from the fact
that, before heavy metal occlusion can occur, the heavy metal ions
must first be drawn to and strongly held by the anions at the
surface of the carrier precipitate. When the carrier precipitate
cations are ferrous ions, the preferred carrier precipitate anions
are hydroxyl, phosphate, and carbonate ions. When the carrier
precipitate cations are calcium ions, the preferred anions are
hydroxyl, phosphate, carbonate, and sulfate ions. When the carrier
precipitate cations are aluminum, the preferred anions are hydroxyl
and phosphate ions. When the primary precipitate cations are
magnesium, the preferred anions are hydroxyl, phosphate, and
carbonate ions. The preferred carrier precipitates are aluminum
hydroxide, ferric hydroxide, calcium sulfate, iron phosphate, and
calcium phosphate, with ferric hydroxide being most preferred.
The operating conditions are also generally controlled so as to
produce a carrier precipitate particle surface which is conducive
to the adsorption of heavy metal ions. As explained above, the
carrier precipitate anion is chosen from among those anions which
form strong bonds with the contaminant heavy metal ions. In
addition, the concentration of carrier precipitate precursor anions
in solution is maintained in most cases at levels sufficiently in
excess of the concentration of the carrier precipitate precursor
cations so as to assure that the carrier precipitate particle
surface is anionic. The anionic particle surface attracts the heavy
metal ions, binds them (adsorption), and makes them available for
incorporation within the precipitate structure (occlusion). When
hydroxyl ions are the chosen carrier precipitate anions,
maintaining such anion excess is a matter of pH control. Where
ferric hydroxide is the chosen carrier precipitate, solution pH
during coprecipitation is maintained above about 6 because
solutions which are more acidic cause the ferric hydroxide
precipitate surface to take on a cationic character.
In general, the larger the carrier precipitate surface area, the
more heavy metals are removed from solution. Thus, the carrier
precipitate and the conditions of operation are preferably chosen
so as to maximize the surface area of each unit mass of
precipitate. The total mass quantity of produced carrier
precipitate is thereafter controlled, where possible, to the
minimum value sufficient to remove the requisite quantity of heavy
metals.
The carrier precipitate is generally formed as rapidly as possible
because the removal of heavy metal ions by both the adsorption and
occlusion mechanisms is markedly greater at higher precipitation
rates. Typically, about 95 percent of the carrier precipitate is
formed within about 15 minutes, preferably within about 10 minutes,
and more preferably within about 5 minutes. The adsorption of heavy
metal ions is increased by an increase in the precipitation rate
because adsorption is surface area-dependent. When the carrier
precipitate is formed rapidly, it forms as a large number of small
individual particles, each having a high surface area-to-mass
ratio. By relative comparison, when the carrier precipitate is
formed slowly, it forms as a small number of large particles, each
having a low surface area-to-mass ratio. Thus, for a given mass of
carrier precipitate precursors, the faster the precipitate is
formed, the larger is the combined surface area of the resulting
precipitate particles.
The occlusion of heavy metal ions is increased by an increase in
precipitation rates because occlusion is adsorption-dependent and
diffusion time-dependent. As alluded to above, heavy metal ions are
more likely to be occluded within the carrier precipitate when they
are first adsorbed at the carrier precipitate surface. Thus, the
number of heavy metal ions occluded within the carrier precipitate
is proportional to the number of heavy metal ions adsorbed onto the
carrier precipitate surfaces during the growth of the carrier
precipitate particles. The number of heavy metal ions which are
occluded within the carrier precipitate is inversely proportional
to the relative ionic diffusion times available in the vicinity of
the forming carrier precipitate. Heavy metal ions, which initially
bond with precipitate surface anions and which might otherwise be
eventually incorporated as a part of the particle framework, tend
to be displaced by competing carrier precipitate precursor cations
which diffuse to the precipitate surface. Thus, if the rate of
carrier precipitate formation is relatively fast with respect to
the rates of ionic diffusion near the forming particle surfaces,
the localized diffusion times are relatively small and more heavy
metals are occluded.
The choices of carrier precipitate and operating procedures are
therefore preferably made, in part, so as to maximize the rate at
which the carrier precipitate is formed. In the preferred
embodiment wherein the carrier precipitate is ferric hydroxide, the
precipitation rate depends on two reactions, the oxidation of
ferrous ions to ferric ions and the reaction of ferric ions with
hydroxyl ions. The precipitation rate is almost solely controlled
by the oxidation reaction since oxidation is much the slower of the
two reactions. Thus, the basic strategy is to maximize the rate of
oxidation. Accordingly, in the case of ferrous ions, substantially
all the ferrous ions in the solution are oxidized to ferric ions
within about 30 minutes. Preferably, the oxidation time is less
than 15 minutes, and more preferably less than 10 minutes. In order
to obtain this oxidation rate, the oxidant is rapidly introduced
into the aqueous solution. Since the more oxidant introduced into
the solution, the faster the oxidation rate, the amount of oxidant,
when air, introduced into the solution is typically at least about
1 liter of air, preferably at least about 2 liters of air, more
preferably at least about 4 liters of air, and even more preferably
at least about 10 liters of air per 1000 ppm ferrous iron initially
present in the solution before the introduction of oxidant when
operating on a batch basis. However, when operating on a continuous
basis, the above amounts of air are per 1000 ppm ferrous present,
on an average, in the feed stream to the reactor. In rate terms,
when the oxidant is air, the air is generally introduced into the
solution at a rate of at least about 10, more typically about 50,
preferably about 90, and even more preferably about 200 liters of
air per hour per liter of solution per 1000 ppm ferrous iron
(1/hr/1/1000 ppm ferrous iron) present in the solution at the
beginning or substantially at the beginning of the residence time
of the solution in the precipitation vessel 16 when operating on a
batch basis. However, when operating on a continuous basis, the
rate of air introduction is per 1000 ppm ferrous iron present, on
an average, in the feed stream entering the precipitation vessel
16.
The oxidation reaction is also accelerated as the solution pH is
raised. Accordingly, it is preferred to maintain the pH of the
reaction medium as high as possible during the introduction of the
oxidizing agent.
In addition, the oxidation reaction is accelerated by the presence
of a suitable catalyst. Most soft Lewis bases can be employed as
suitable catalysts, with iodine and oxygen-containing soft Lewis
bases being preferred. The most preferred catalyst is ferric
hydroxide since it is manufactured in situ by the method of the
invention. However, no addition of catalyst is usually necessary
because ferric hydroxide is formed in situ and is thereafter
constantly present within the precipitation vessel 16.
In addition to promoting rapid precipitation, the rapid oxidation
of the ferrous ions may promote occlusion in another way. In
aqueous solutions, ferrous ions tend to form soluble complexes with
heavy metal and hydroxyl ions. If the ferrous ions of such
complexes are rapidly oxidized to ferric ions, these complexes tend
to precipitate out of solution en masse, including the originally
complexed heavy metal ions which, during precipitation, become
occluded within the precipitate.
The operating conditions are also preferably controlled to minimize
extraneous reactions which interfere with the heavy metal
coprecipitation. Thus, the concentration of superfluous ions is
maintained as low as practical (for instance, by dilution of the
waste stream) since such ions interact with carrier precipitate
precursor and heavy metal ions, thereby impeding the
coprecipitation reactions. Also, the pH of the aqueous solution is
maintained at sufficiently low levels to minimize the effects of
complexing agents which solubilize heavy metal ions at high pH. For
instance, certain nitrogenous compounds, including ammonia, complex
with several heavy metal ions, especially with copper, nickel, and
zinc, at pH levels above about 8. Where such complexing agents are
present in the aqueous solution and where "complexable" heavy metal
ions are also present, the pH of the aqueous solution is therefore
maintained below about 8, and preferably below about 7.5.
Accordingly, in the embodiment of the invention illustrated in the
drawing (wherein aqueous ammonia is used as a base), the pH of the
waste solution in the precipitation vessel 16 is preferably
maintained between about 6.5 and about 7.5 in order to oxidize the
ferrous ions as rapidly as possible but not form significant
quantities of ammonia-heavy metal complexes. Since this pH
operating range is relatively narrow, since the relation between
dissolved ammonia and solution pH is very sensitive within this
operating range, and since the pH of the acid waste stream
generated in the industrial process 6 can fluctuate significantly,
it is sometimes preferable as shown in the drawing to accomplish pH
control in two steps. First, the pH of the acid waste stream is
raised to pH levels between about 5.5 and about 6.5 within the
vessel 14. Second, the solution pH is carefully raised to operating
levels (e.g., between about 6.5 and about 7.5, but most preferably
between about 7.5 and about 8) within the precipitation vessel 16.
However, if possible, it is generally preferred to add the waste
stream directly to the precipitation vessel 16 and adjust the pH of
the waste stream only within the precipitation vessel 16, i.e., to
avoid two step pH control.
Accordingly, the aqueous waste solution is preferably introduced
into the precipitation vessel 16 while maintaining the vessel 16
under conditions which substantially and immediately subject
essentially all of the ferrous ions entering the vessel 16 to
oxidizing conditions causing rapid oxidation of the ferrous ions
while preferably controlling the pH so a to coprecipitate a
substantially completely amorphous precipitate comprising a
substantial amount of ferric hydroxide coprecipitated with a
substantial proportion of the heavy metals.
The method of the invention is unique in its effectiveness for
removing substantial quantities of heavy metals from aqueous
solutions at near neutral pH. The effective removal of heavy metals
at near neutral pH is most advantageous to the industrial operator.
It substantially reduces problems caused by the aforementioned
presence of heavy metal complexing agents, especially nitrogenous
complexing agents, which are commonly found in aqueous waste
streams. Accordingly, it allows the additive use of aqueous
ammonia, a most cost-effective base. The ability to operate at near
neutral pH also eliminates the need to add neutralizing acid to the
treated effluent before disposal. Likewise, it markedly reduces the
consumption of fresh acid necessary to reacidify the treated
effluent when the effluent is employed as a recycle acid. Finally,
operating at near neutral pH produces a precipitate which settles
faster than precipitates formed at higher pH levels. This last fact
allows the operator to separate the treated effluent from the
nascent precipitate particles with smaller and less expensive
separating equipment than would be required by other precipitation
methods.
The preferred embodiment of the invention employing ferric
hydroxide as the carrier precipitate has the additional unique
advantage over conventional hydroxide precipitation methods of
requiring less additive base to precipitate a given quantity of
iron and contaminant heavy metals. In conventional
alkali-precipitation methods, base is consumed in the precipitation
of individual iron ions, and additional base is consumed in the
precipitation of individual heavy metal ions. In the embodiment of
the invention illustrated in the drawing, base is consumed in the
precipitation of individual ferric ions, but little additional base
is required to precipitate the heavy metal ions. Furthermore, in
this preferred embodiment of the invention, a substantial
proportion of the base required by the process is manufactured by
the process itself. For every ferrous ion that is oxidized to a
ferric ion, a hydroxyl ion is produced pursuant to the following
reaction:
The method of the invention is also advantageous in that chromium
ions can be removed from an aqueous waste solution without having
to first reduce the hexavalent chromium ions to trivalent ions.
Typically, in a preferred embodiment of the invention, more than
about 95 percent, and preferably more than 99 percent, of the
hexavalent chromium is removed from the aqueous waste solution at
the same time and by the same method as are other heavy metals.
Thus, the method of the invention eliminates the need for
segregating and separately treating hexavalent chromium containing
waste streams, and saves the costs of acid, base, and reducing
agent required by such treatment.
The method of the invention is further advantageous in that several
heavy metals in the waste solution--and oftentimes each and all of
the heavy metals--can be removed by at least about 95%, sometimes
at least by about 99%, with iron also being removed by at least
about 95% and oftentimes by virtually 100%. The examples hereafter
show how readily the invention removes two, three, and four heavy
metals simultaneously by more than about 95%, with three examples
(i.e., Examples 1, 4, and 10) showing the removal of five such
heavy metals, with a concomitant reduction in the iron by about
100%. In addition, the data in Examples 6 to 10 establish that,
under the preferred operating conditions, each of the heavy metals
(and iron) can be reduced to a concentration less than about 1
ppmw--even when the initial concentrations total more than about
400 ppmw. In addition, the present invention is capable of reducing
the concentration of the heavy metals in the treated waste water to
below their thermodynamic equilibrium levels. Typically, at least
one heavy metal is reduced to below its thermodynamic equilibrium
concentration level. Preferably, the concentrations of a plurality,
e.g., at least 3 or 4, and most preferably all, of the heavy metals
are reduced to below their thermodynamic levels.
In one version of the present invention, to further reduce the
concentration of contaminants in the effluent from a first
treatment process embodying features of the present invention, the
effluent is subjected to a second treatment process in accordance
with the method of the present invention. In other words, although
in the vast majority of cases only a single operating stage with a
single precipitation reactor vessel 16 will be needed, one may
operate serially with a plurality of stages, each treating the
effluent of the preceding stage.
Finally, the method of the invention is superior to conventional
precipitation methods in that it produces less precipitate sludge.
The lower sludge production stems, in part, from the fact that the
volume of sludge is smaller when several metals are coprecipitated
than when those metals are precipitated separately. The difference
in sludge-production is even greater when the method of the
invention and conventional precipitation methods are compared in
the treatment of aqueous solutions containing significant
quantities of heavy metal complexing agents. As stated above, the
conventional treatment of such aqueous solutions requires the use
of large quantities of calcium hydroxide and results in the
formation of sludge volumes which are even larger than normal.
The invention can be further understood by considering the
following specific examples which are illustrative of specific
modes of practicing the invention and are not intended as limiting
the scope of the appended claims.
EXAMPLE 1
Two aqueous waste solution samples were obtained from a commercial
electroplating process. The first sample was taken from a 10,800
gal/day waste water stream containing approximately 0.6 weight
percent total dissolved solids. The second sample was taken from a
1,400 gal/day waste acid stream containing approximately 15 weight
percent total dissolved solids.
Twenty-three milliliters of the waste acid sample was mixed in a
mechanically agitated beaker with 177 ml of the waste water sample
to yield 200 ml of a combined waste solution sample. Immediately
thereafter, 4.5 ml of a 28 weight percent aqueous ammonia solution
was rapidly added to the beaker. Thereupon, 25 ml of an aqueous
solution containing approximately 4 weight percent of a ferric
hydroxide-heavy metal precipitate was added to the beaker.
Immediately thereafter, air was commenced to flow through a
sintered glass tube at the bottom of the beaker so as to cause air
bubbles to rise through the solution. A precipitate was observed to
appear within the solution, and the solution pH was observed to
begin dropping. Aqueous ammonia wa periodically added to the
solution over about the next 30 minutes in order to maintain the
solution pH between about 7.0 and about 7.5.
After about 30 minutes, the solution pH was observed to stabilize.
The flow of air was ceased but the solution was agitated for an
additional 30 minutes.
Thereafter, a pipette was used to extract a sample of the
solution-precipitate mixture. The precipitate particles were
removed by filtering the sample through #41 (coarse) filter paper.
The resulting filtrate was clear and colorless.
The filtrate was analyzed for heavy metals content and compared to
the heavy metal content of the original combined waste solution
sample. The results are presented in TABLE 1.
TABLE 1
__________________________________________________________________________
Metals Concentrations, ppmw Solution Sample Cd Cr Cu Fe Ni Pb Zn pH
__________________________________________________________________________
Untreated 0.6 2.3 5 4,850 3.5 106 953 3.5 combined waste solution
Treated <0.1 <0.1 1.4 <0.1 0.2 <0.5 2.8 7.3 filtrate
after treatment Percent >98.3 >95.7 72.0 100 94.3 >99.5
99.7 NA.sup.1 Removal
__________________________________________________________________________
.sup.1 NA denotes not applicable.
EXAMPLE 2
A 50 ml sulfuric acid waste sample from a commercial electroplating
process was diluted with distilled water to 200 ml. The waste
solution was neutralized by the addition of 17.5 ml of a 28 weight
percent aqueous ammonia solution, whereby the solution pH was
observed to be 7.7.
The slurry was added to a mechanically agitated beaker containing
22 ml of an aqueous ferric hydroxide slurry. Air was commenced to
flow through a sintered glass tube at the bottom of the beaker so
as to cause air bubbles to rise through the solution. Aqueous
ammonia was periodically added to the solution so as to maintain
the solution pH between 7.0 and 7.5.
About 15 minutes after neutralization, the pH of the solution was
stabilized to about 7.35 and a precipitate was observed within the
solution. Air dispersion was terminated but mechanical agitation
was continued. A sample of the solution-precipitate mixture was
extracted with a pipette and filtered through coarse filter paper.
About 25 minutes after neutralization, a second sample was
similarly extracted and filtered. The filtrates from both samples
were clear and colorless.
The filtrates from both samples were analyzed for heavy metals
content. A comparison of the heavy metals content of the filtrates
to the heavy metals content of the original acid waste sample is
summarized in TABLE 2.
TABLE 2
__________________________________________________________________________
SO.sub.4 Metals Concentrations, ppmw Conc. Solution Sample Cd Cr Cu
Fe Ni Zn ppmw pH
__________________________________________________________________________
Untreated 0.75 8.75 2.0 3,625 8.5 132 66,250 N.T..sup.1 acid waste
Treated fil- <.01 <.01 0.2 <.01 1.7 2.1 N.T. 7.35 trate 15
min. after neu- tralization Percent Re- >98.7 >99.9 90.0 100
80.0 98.4 NA NA moval After 15 min. Treated fil- <.01 <.01
0.2 <.01 1.7 2.1 N.T. 7.35 trate 25 min. after neu- tralization
__________________________________________________________________________
.sup.1 N.T. denotes that the parameter was not tested.
EXAMPLE 3
A 200 ml volume of a heavy metals-containing acid solution was
prepared. The solution was placed in a mechanically agitated beaker
and neutralized to a pH between about 7.0 and about 7.5.
Immediately thereafter, 0.142 gr of ferric oxide was added to the
solution and air was commenced to bubble through the solution.
Additional base was periodically added to maintain the solution pH
between 7.0 and 7.5. About 7 minutes after neutralization, the
solution pH was observed to have stabilized and precipitate
particles were visible within the solution. A sample of the
solution-precipitate mixture was extracted and filtered with coarse
filter paper. The filtrate, which was clear and colorless, was
analyzed for heavy metals content.
The solution-precipitate mixture was agitated for an additional 15
minutes (a total of 22 minutes after neutralization) without
addition of base or air. A second sample was extracted and filtered
through coarse filter paper. The filtrate, which was clear and
colorless, was analyzed for heavy metals content.
The solution-precipitate mixture was agitated for an additional 7.5
hours (a total of 18 hours after neutralization). A third sample
was extracted and filtered, and the clear, colorless filtrate was
analyzed for heavy metals content.
A comparison of the results of the filtrate heavy metals analyses
to the heavy metals content of the original acid solution is set
forth in TABLE 3.
TABLE 3 ______________________________________ Metals
Concentrations, ppmw Solution Sample Cd Cr Cu Fe Ni Zn pH
______________________________________ Un- 102 74 96 5,684 96 101
N.T. treated acid solution Treated 4 <.01 0.2 <.01 3.4
<0.1 7.5 filtrate 7 min. after neu- trali- zation Treated 7
<.01 0.09 <.01 7.3 0.6 7.5 filtrate 22 min. after neu- trali-
zation Percent 93.1 >99.9 99.9 100 92.4 99.4 NA Removal After 22
min. Treated 9.3 <.01 0.09 <.01 6.7 0.8 6.9 filtrate 18 hr.
after neu- trali- zation ______________________________________
EXAMPLE 4
A sample of an acid waste solution from a commercial galvanizing
process was placed in a mechanically agitated beaker, neutralized
with aqueous ammonia, and oxidized with bubbled air while
maintaining the solution pH between about 7.0 and about 8.2. When
the solution pH stabilized, addition of aqueous ammonia and air was
discontinued except as noted below.
A solution-precipitate sample was extracted with a pipette 7
minutes after neutralization. The sample was filtered and analyzed
for heavy metals. A second sample was also extracted (60 minutes
after neutralization), filtered and analyzed for heavy metals.
Additional aqueous ammonia was thereupon added to the solution and
a third sample was extracted (73 minutes after neutralization).
This sample was also filtered and analyzed for heavy metals.
Two additional samples were similarly extracted, filtered and
analyzed for heavy metals. The results of all analyses are
summarized in TABLE 4.
TABLE 4
__________________________________________________________________________
Metals Concentrations, ppmw Solution Sample Cd Cr Cu Fe Ni Pb Zn pH
__________________________________________________________________________
Untreated 6.25 256 72 54,400 206 5,125 354 N.T. acid waste Treated
fil- <.01 <0.01 5.6 1.3 6.6 <0.5 1.2 7.0 trate 60 min.
after neu- tralization Percent re- >99.8 100 92.2 100 96.8 100
99.7 NA moval 60 min. after neutraliza- tion Treated fil- <.01
<0.01 7.2 <0.01 3.2 <0.5 0.6 7.8 trate after base added,
73 minutes after neu- tralization Treated fil- <.01 <0.01 5.4
<0.01 1.5 0.6 0.6 7.6 trate 120 min. after neu- tralization
Treated fil- 0.2 <0.01 0.9 0.4 0.5 <2.5 <0.4 N.T. trate 2
mos. after neu- tralization
__________________________________________________________________________
EXAMPLE 5
A 50 ml acid waste sample from a commercial electroplating process
was added to a mechanically agitated beaker and diluted with
distilled water to 200 ml. To this diluted solution was added 18 ml
of a 28 weight percent aqueous ammonia solution, whereby the
solution pH was observed to be 7.0. An additional 10 weight percent
iron was added to the solution in the form of ferric hydroxide
particles. Immediately thereafter, air was bubbled through the
solution. Aqueous ammonia was periodically added to maintain the
solution pH between 7.0 and 7.5.
After about 8 minutes, the solution pH was observed to have
stabilized. A sample was extracted with a pipette, filtered, and
analyzed for heavy metals.
Air dispersion was halted but solution agitation was continued. The
pH of the solution was raised to about 9.0. A second sample was
immediately extracted, filtered, and analyzed for heavy metals.
The solution was agitated for an additional 60 minutes during which
time aqueous ammonia was periodically added to maintain the pH at
about 9.0. A third sample was extracted, filtered, and analyzed for
heavy metals.
The results ar summarized in TABLE 5.
TABLE 5
__________________________________________________________________________
Metals Concentrations, ppmw Solution Sample Cd Cr Cu Fe Ni Pb Zn pH
__________________________________________________________________________
Untreated 0.75 8.75 2 3,625 8.5 132 132 N.T. waste acid 8 min.
after 0.04 <0.01 0.2 0.3 0.7 <0.05 2.4 7.0 neutraliza- tion
10 minutes 0.1 <0.01 1.6 0.3 3.3 0.05 30 9.0 after neu-
tralization Percent re- 86.7 >99.9 20.0 100 61.2 100 77.3 NA
moval 10 min. after neu- traliza- tion 70 min. 0.1 <0.01 1.6 0.3
2.6 <0.05 30 9.0 after neu- tralization
__________________________________________________________________________
EXAMPLE 6
The ferrous ion concentration of an acidic waste water solution
(having a composition shown in Table 6, below) was increased to 852
ppm by addition of a concentrated ferrous chloride solution,
yielding a mass ratio of 3.2 ferrous ion to heavy metal. The pH of
the waste water solution was then raised to 7.8 using a solution of
sodium hydroxide as base. A portion (480 ml) of the resultant
solution was charged to a laboratory reactor vessel, air was
sparged in at the rate of 6 liters per minute, and sodium hydroxide
solution was added as necessary to maintain the pH at 7.8. The
solution was kept under conditions of high agitation during the
oxidation-precipitation reactions, and there was no addition of any
solid matter to the solution. The oxidation precipitation reactions
were allowed to proceed for 15 minutes, after which a sample of
product solution was analyzed. The results of the analysis are also
set forth in the following Table 6:
TABLE 6 ______________________________________ Waste Product
Percent Water Solution Removal, %
______________________________________ Cr, ppm 214 0.03 >99.9
Cu, ppm 1.5 <0.01 >99.3 Ni, ppm 46 0.2 99.6 Mn, ppm 6.3 0.2
96.8 Fe+2, ppm 217 0.03 >99.9 Total Heavy 484.8 <0.47
>99.9 Metal, ppm ______________________________________
The data in Table 6 show that the present invention removes an
assortment of heavy metals to extremely low levels.
EXAMPLE 7
An aqueous waste solution having a pH of 1.0 contained the
following metals in the concentrations shown:
______________________________________ Calcium 375 ppm Lead 189 ppm
Chromium 0.6 ppm Zinc 19 ppm Copper 2.3 ppm Iron 1,370 ppm
______________________________________
Upon chemical analysis it was found that 83% of the iron existed in
the solution as ferrous ion.
Sixty gallons of the waste solution were introduced into a tank,
and while air was introduced by a sparger and the efficiency of the
air oxidation increased by mechanical dispersion (i.e., a mixer
outfitted with a high shear turbine), the pH of the solution was
increased to 7.5 and maintained at that level by addition of
ammonia. Within 7 minutes, it was apparent by visual inspection
that a red precipitate had formed and the reaction was essentially
complete. In addition, the pH held constant after 7 minutes (i.e.,
little or no additive base was required to maintain the pH at 7.5),
also indicating that the reaction was complete Nevertheless, the
oxidation and agitation were maintained for another 223 minutes,
the temperature of the solution being about 75 F. throughout. At
the end of the 223 minutes, the precipitate still appeared visually
the same as after the first 7 minutes. A sample of this precipitate
at the end of the run was recovered, frozen in liquid nitrogen to
prevent any altering of its character, freeze-dried under low
pressure, and then analyzed by X-ray diffraction analysis. The
sample evidenced no sign of crystallinity and, therefore, was
determined to be completely amorphous. Also, the sample did not
respond to the presence of a magnet.
The above Example 7 demonstrates, inter alia, that the precipitate
formed in the process of the present invention is completely
amorphous and not an intermediary to the production of a
crystalline precipitate.
EXAMPLE 8
Sixty gallons of the aqueous solution described in Example 7 were
introduced into the reactor vessel employed in Example 7, but the
temperature in the reactor vessel was maintained at about
100.degree. F. (38.degree. C ). Oxidation with air sparging and
dispersion was as described in Example 7, and the pH was initially
controlled to a value of around 7.75 by addition of ammonia. The
reaction was essentially complete within about 11 minutes. (This
was proven by the fact that a sample of the solution was taken,
filtered, and the resulting filtrate was clear, remained clear for
one hour with no change in pH, and contained only 0.2 ppm copper,
less than 0.3 ppm lead, less than 0.5 ppm iron, and 0.3 ppm zinc.
Also, the pH was stable within 11 minutes, requiring no further
base addition). Four minutes later, continuous operation began,
with the feed into and out of the reactor vessel of the aqueous
solution being 1 gpm, so that the residence time therein was 60
minutes pH was maintained at about 7.5. Two samples of the contents
of the reactor vessel were taken after 70 and 75 minutes of
continuous operation, freeze-dried as in Example 7 and analyzed by
X-ray diffraction analysis. Both samples showed no evidence
whatever of crystallinity. Again, the samples were completely
amorphous. Further evidence of this was that inspection by high
resolution microscopy showed no discernible discrete particles of
regular shape and size.
The above Example 8 demonstrates, inter alia, that the precipitate
formed when conducting the process of the present invention at
about 100. F. is completely amorphous and not an intermediary to
the production of a crystalline precipitate. In addition, the
method of the invention is useful for removing at least about 91.3
weight percent copper, at least about 99.8 weight percent lead, at
least about 99.9 weight percent iron, and at least about 98.4
weight percent zinc.
EXAMPLE 9
Again, 60 gallons of the aqueous solution described in Example 7
were introduced into the reactor vessel used in Examples 7 and 8,
but this time the temperature was maintained at 150.degree. F.
(66.degree. C.). With air sparging, mechanical dispersion, and
ammonia addition as in Examples 7 and 8, the reaction appeared
complete about 20 minutes after the pH was adjusted to 7.5, i.e.,
after 20 minutes little or no base was needed to maintain pH,
thereby indicating that the oxidation reaction was over.
Nevertheless, oxidation by sparging and mechanical dispersion was
continued for one hour, at which time a sample of the contents of
the vessel was taken, filtered, and the precipitate freeze-dried
and analyzed by X-ray diffraction while the filtrate was analyzed
for metals. Again, the precipitate was found to be noncrystalline
and completely amorphous. The filtrate was found to contain only
trace concentrations of metals, i.e., 0.3 ppm copper, less than
0.05 ppm lead, 0.01 ppm iron, 0.6 ppm zinc, and less than 0.01 ppm
chromium.
Example 9 therefore demonstrates, inter alia, that even when run at
about 150.degree. F., the process of the instant invention yields a
completely amorphous precipitate and does not form an intermediary
to the production of a crystalline precipitate. In addition, at
least about 87.0 weight percent copper, at least about 99.9 weight
percent lead, at least about 99.9 weight percent iron, at least
about 96.8 weight percent zinc, and at least about 98.3 weight
percent chromium can be removed from a contaminated waste
solution.
EXAMPLE 10
One liter of an untreated waste water having the metals content
shown in Table 7 was introduced into a laboratory-size reactor
vessel. It was allowed to come to room temperature. Air sparging
through the bottom of the vessel at a rate of 493 l/hr/l with
mechanical dispersion, i.e., a laboratory mixer, was then
commenced. The air was sparged through a fritted disk to produce
small bubbles. The pH was then raised to 7.5 and held at that value
by periodic addition of caustic soda, as necessary, producing a
brick red precipitate.
Samples of the solution containing the precipitate were taken at
10, 15, 30, and 45 minutes after the base was first added. The four
samples of solution containing the precipitate were then filtered
through a Whatman #41 brand filter paper, and two samples of each
filtrate were taken, so that a total of eight samples were
obtained. To one set of the four samples, hydrogen peroxide was
added to detect the presence of ferrous ion. No precipitate formed
in any of the samples, thus proving that at the 10-, 15-, 30-, and
45-minute intervals all the ferrous ions had oxidized.
The second set of samples was allowed to stand exposed to the air
for 1 hour in vials, after which they were capped. The second set
of samples were acidified and analyzed for metals content. The data
so obtained are shown in Table 7. Not only was iron removed in this
Example 10 to extremely low levels but also all the other heavy
metals. There were virtually no heavy metals left in the aqueous
filtrate, and the metals data in Table 7 are all essentially below
or close to their analytical detection limits.
Also, the four samples of the precipitate obtained on the Whatman
#41 filter paper were subjected to X-ray diffraction analysis and
found to contain no crystalline materials, i.e., they were
completely amorphous.
TABLE 7 ______________________________________ Percent Metal
Concentration In Ppmw After A Removal Total Elapsed Oxidation Time
(Min.) of After 45 Metal 0.sup.1 10 15 30 45 Min.
______________________________________ Cd 0.29 0.03 0.03 0.03 0.03
89.7 Cr 1.22 0.005 <0.004 <0.004 <0.004 >99.7 Cu 7.65
0.07 0.05 0.03 0.02 99.7 Fe 5,310 0.03 0.02 0.02 0.02 100 Pb 430
0.11 0.006 0.005 0.006 100 Ni 2.11 0.04 0.04 0.04 0.03 98.6 Zn 570
0.56 0.56 0.7 0.59 99.9 pH.sup.2 -- 7.5 7.5 7.5 7.5 NA
______________________________________ .sup.1 Analysis of untreated
waste water solution. .sup.2 pH of reactor contents when sample
taken.
EXAMPLE 11
In this experiment, Example 10 was continued under the same
oxidizing conditions, but at a temperature of 60.degree. C. for
another 3 hours (i.e., a total oxidizing time of 3 hours and 45
minutes, the first 45 minutes at room temperature and the last 3
hours at 60.degree. C.). The brick-red precipitate remained intact
and, as evidenced by no significant changes in pH and
oxidation-reduction potential, there was no evidence of further
reaction. In addition, X-ray analysis of the precipitate at the end
of the 3 hours of high temperature oxidation showed that the
precipitate was still completely amorphous.
Again, as with Examples 7-9, the data of Examples 10 and 11 show
that the precipitate formed in the process of the present invention
is completely amorphous and not an intermediate to the formation of
a crystalline, magnetic precipitate.
EXAMPLE 12
In this experiment, another 1 liter of the untreated waste water of
Example 10 was introduced into the same laboratory reactor vessel
employed in Example 10 and allowed to come to room temperature.
Caustic soda was added and the pH was adjusted to 7.5. The contents
of the solution were allowed to stand and form a ferrous hydroxide
suspension.
After forming the ferrous hydroxide suspension, the reaction
conditions were altered to subject the contents of the vessel to
the method of the invention. Specifically, air was sparged into the
reactor vessel at a rate of 493 l/hr/l and the pH was maintained at
about 7.5 so as to induce rapid and complete oxidation of ferrous
ions. The ferrous hydroxide suspension was rapidly converted to the
brick-red amorphous precipitate described in Example 11.
Example 12 demonstrates that rapid oxidation is essential to
forming the amorphous precipitate desired in the process of the
instant invention.
EXAMPLE 13
A commercial facility treats acidic waste water containing iron,
lead, and zinc contaminants by bringing the pH up to 8.0 with lime
followed by natural aeration in a large settling pond. The same
waste was treated, on a laboratory scale, by a process within the
scope of the present invention wherein the waste solution was
subjected to rapid oxidation with an air stream while the pH was
controlled at about 8.0 with lime. Both processes produced a sludge
comprising ferric hydroxide.
Various comparisons were then made:
(1) Settleability. The rate at which a precipitate settles can
affect the time a sludge needs to be held in a settling zone before
a purified liquid can be recovered. A precipitate from the
conventional process was blended with deionized water so as to have
a total solids content of 770 ppm--equal to that of a sample of
precipitate (obtained by the process of the present invention) in
water. The samples were put into 100 ml graduated cylinders and 3
ppm of a standard flocculating agent (Nalco 7173 brand
polyelectrolyte) was added to each cylinder. Each cylinder was then
capped and simultaneously (a) inverted 5 times and then
simultaneously (b) placed on a bench top. The settling rate for
precipitate obtained via the process of the present invention was
about eight times faster than for the conventional precipitate.
(2) Compaction Volume. Compaction volume of a waste water treatment
sludge is of special importance in reducing the cost of
landfilling, e.g., the less volume, the less a disposal problem.
Two samples of (a) the precipitate from the conventional process
and (b) the precipitate of the process of the present invention
were put into four different 25 ml graduated cylinders and brought
to equal total solids levels. One sample of each precipitate was
then combined with 3 ppm Nalco 7173 brand polyelectrolyte. Next,
all four samples while capped were simultaneously (a) inverted 3
times, (b) then put on a bench top, and (c) allowed to sit for 3
weeks. The precipitate from the exemplary process of the present
invention occupied 1/3 the volume of the conventionally produced
precipitate containing an approximately equal amount of iron.
(3) Dewaterability. The less water a precipitate takes up, i.e.,
the less gelatinous it is, the easier it is to filter through
conventional filter presses. In the conventional process described
above, the final "dewatered" product contains 75 to 85% water
whereas sludges produced from the exemplary process of the present
invention typically run between 55 and 65% water. The difference
between such values is that the conventional process requires high
pressures and long filtration times and the precipitate tends to
bind to the filter cloths and proves difficult to remove. In
contrast, precipitates from the exemplary process of the present
invention come away cleanly from the filter cloths. In addition,
lower pressures and less time are required for filtration.
Example 13 accordingly demonstrates the improved settleability,
compaction volume, and dewaterability characteristics of the
precipitate formed by the process of the instant invention.
In addition to removing heavy metals, the process of the present
invention is also useful for reducing the concentration of light
metals (i.e., metals that are not heavy metals), especially
aluminum and beryllium, as well as cyanide, phenolics, oil and
grease, TSS contributors, BOD contributors, COD contributors, and
TOC contributors present in the aqueous solution. Furthermore, any
combination of these contaminants as well as any combination of
these contaminants and heavy metals can be removed simultaneously
from a solution in the same vessel. The process steps as well as
the pH, oxidation rate, and reduction in individual contaminant
concentration levels are substantially the same as discussed above
with respect to heavy metals. In addition, the molar ratio of
ferrous ions to light metal ions and/or cyanide ions is the same
ratio as discussed above with respect to the molar ratio of ferrous
ions to heavy metal ions.
However, with respect to contaminants selected from the group
consisting of phenolics, oil and grease, TSS contributors, BOD
contributors, COD contributors, and TOC contributors, the amount of
ferrous ions employed to remove these contaminants from a solution
is best expressed in terms of weight ratio, as opposed to molar
ratio used above. Generally, the weight ratio of the ferrous ions
to the total amount of contributors from this group of contaminants
is at least about 1:1, but typically less than about 10:1, and
preferably about 4:1 to about 6:1. When contaminants selected from
a first group consisting of light metals, cyanide, and/or heavy
metals and contaminants selected from a second group consisting of
phenolics, oil and grease, TSS contributors, BOD contributors, COD
contributors, and TOC contributors are both present in the
solution, the ferrous ion concentration generally is equal to at
least the sum of (A) the molar concentration of the contaminants
selected from the first group plus (B) the weight of the
contaminants selected from the second group. Typically, the ferrous
ion concentration of the solution is equal to less than about ten
times that sum. Preferably, the ferrous ions are present in the
solution in a concentration that is about 2 to about 8, and more
preferably about 4 to about 6, times the above sum.
As in the case of heavy metals, the method of the invention is also
advantageous in typically removing at least about 95 percent, and
preferably at least about 99 percent, of each these other
contaminants present in the waste solution. For example, a waste
stream containing at least about 0.1 ppmw, or even about 1 ppmw, or
even over about 10 ppmw aluminum, when treated by the process of
the present invention can have its aluminum content reduced below
about 0.05 ppmw. In fact, the process of the instant invention can
reduce the concentration of contaminants in a waste stream to the
following levels:
______________________________________ Level, ppmw Contaminant
Typical Preferred More Preferred
______________________________________ Ag <0.05 <0.01
<0.005 Al <0.06 <0.04 <0.02 As <0.02 <0.01
<0.005 Cd <0.02 <0.01 <0.005 Cr <0.01 <0.004
<0.002 Cu <0.02 <0.01 <0.005 Fe <0.02 <0.01
<0.005 Pb <0.01 <0.005 <0.003 Ni <0.1 <0.01
<0.005 Sb <0.5 <0.2 <0.1 Se <0.05 <0.01 <0.005
Sn <0.5 <0.05 <0.03 V <0.004 <0.002 <0.001 Zn
<0.02 <0.005 <0.003 Total Heavy and <1.5 <0.8
<0.5 Light Metals TSS <6 <4 <2 TDS <600 <400
<200 Cyanide <0.04 <0.02 <0.01 BOD <40 <3 <1.5
COD <250 <50 <25 TOC <70 <20 <10 Oil & Grease
<0.1 <0.05 <0.03 Phenolics <1 <0.01 <0.005
______________________________________
The following Examples 14 and 15 are illustrative of some of the
above additional embodiments of the invention, as well as showing
the effectiveness of the invention for removing the heavy metal
selenium.
EXAMPLE 14
Influent and effluent waste water samples from a biotreatment plant
were collected in clean, 1-gallon amber glass bottles with
teflon-lined lids. At the collection points, the bottles were first
flushed with the waste water to be taken, then filled to the top
with a sample to eliminate air space. The bottles were then sealed
and refrigerated at about 4.degree. C. for preservation. Within a
few hours, the refrigerated samples were packaged in ice chests
with chilled blue ice packs wrapped around each bottle. The samples
arrived at the laboratory within 24 hours after collection. On
arrival, the samples were tested for pH, temperature,
oxidation-reduction potential (ORP), and dissolved oxygen. The
bottles were resealed and the samples were stored in the dark at
about 4.degree. C. until further testing. All screening tests were
conducted within 4 days of sample receipt.
Waste Water Characterization
The samples of the waste water were characterized for heavy metals,
oil and grease, inorganic and organic compounds, total solids
(suspended and dissolved), and biochemical oxygen demand. The tests
used are listed in Table 8.
TABLE 8 ______________________________________ Test Analytical
Method ______________________________________ Heavy Metals Selenium
ICP.sup.1 /MS.sup.2 /HGAA.sup.4 Aluminum ICP Iron ICP Vanadium ICP
Arsenic GFAA.sup.3 Mercury GFAA Inorganic Components Cyanide
Distillation/ Colorimetry Soluble Sulfur E = 90.3.sup.5 Thiosulfate
Titration Dissolved Solids (TDS) Gravimetric Organic Components
Total organic carbon (TOC) E-415.sup.5 Phenolics Distillation COD
Colorimetry BOD Colorimetry Bioassay 96-hr static fish kill test
Oil and grease Gravimetric ______________________________________
.sup.1 ICP denotes inductively coupled plasma spectrophotometric
method. .sup.2 MS denotes mass spectrometry. .sup.3 GFAA denotes
graphite furnace atomic absorption method. .sup.4 HGAA denotes
hydride generation atomic absorption method. .sup.5 E# denotes EPA
test methods bearing the particular number.
A summary of the characteristics of both the influent sample and
effluent sample are given in Table 9:
TABLE 9 ______________________________________ Summary of Waste
Water Characteristics Biotreatment Biotreatment Plant Influent,
Plant Effluent, Test mg/l mg/l
______________________________________ Al 0.33 0.12 Fe 2.8 0.16 V
<0.05 <0.05 As <0.002 <0.002 Hg <0.001 <0.001 Se
675 2300 TSS 5 <1 TDS 778 805 Soluble S <0.1 <0.1
Thiosulfate 24 3.6 Cyanide 0.18 0.02 COD 1.9 <1 TOC 113 25.5 BOD
150 15 Phenolics 0.12 <0.005 Oil & Grease 4.8 1.9
______________________________________
Treatability Studies
Laboratory treatability studies included a series of batch tests to
determine the effects of specific conditions upon selenium and
cyanide removal. Specifically, samples (two liters each) of the
biotreatment plant effluent wastewater were treated batchwise in
accordance with the invention to determine the effects of retention
time and pH on the rate and extent of selenium and cyanide removal.
All experiments were conducted at ambient temperature, using a 15
cm in diameter, 25 cm deep bench-scale reactor made of Lucite brand
acrylic resin. The reactor was fitted with four baffles one cm
wide, which extended the full length of its sides, resting on 0.5
cm spacers. The baffles functioned to minimize overdosing. Several
ports were located on the side of the reactor so that continuous
liquid overflow was feasible at several reactor volumes--2,3, and 4
liters. In addition, ports were available for sample collection,
pH, ORP, and temperature probes. Air flow was gauged by a
rotometer-type flow meter and entered the reactor vessel through a
sparge ring in the bottom of the reactor. The air was then
dispersed in the liquid phase with a Lightin R-100 brand, 6.2 cm
diameter, 6-blade radial flow turbine stirrer powered by a 0.05 kw
variable speed motor adjusted to a speed of about 500 rpm.
Approximately 100 ppm of ferrous iron were added and during the
batch runs. The air sparge rate was about 3 l/min for the batch
runs. The agitation was used during the treatments was enough to
disperse the air sparged into the reactor and provide sufficient
mixing for pH control. A pH control setpoint was maintained with a
dilute sodium hydroxide solution.
1) Effects of pH on Selenium Removal
In order to determine the influence of pH on treatability, split
waste water samples were taken from the biotreatment plant effluent
sample and neutralized to a specific pH (either pH 6.5 or 7.8)
using the sodium hydroxide solution.
Batch treatments were then carried out while maintaining the
solution within .+-.0.2 pH units of the initial setpoint. The
results depicted in Table 10 indicate that there is no significant
effect of pH upon selenium removal within the pH range of 6.5 and
7.8.
TABLE 10 ______________________________________ Effect of pH on
Selenium Removal (Se) mg/l (Se) mg/l Sampling Time (min.): at pH
6.5 at pH 7.8 ______________________________________ 0 2300 2300 30
140 93 60 81 82 120 79 79
______________________________________
2) Effects of Retention Time on Selenium Removal
To test the effect of contact time on selenium removal, batch
experiments employing two aliquot from the biotreatment plant
effluent were conducted by subjecting each aliquot to varying
hydraulic retention times. The pH of each aliquot was adjusted to
pH 6.5. The results are set forth in Table 11:
TABLE 11 ______________________________________ Effect of Retention
Time on Selenium Removal Aliquot A Aliquot B Sampling Time (min.):
Se, mg/l Se, mg/l ______________________________________ 0 2300
2300 30 82 140 60 79 81 120 79
______________________________________
Removal of selenium to residual level was completed within the
first 60 minutes. Therefore, extensive hydraulic retention time is
not necessary.
3) Effects of Continuous Flow on Selenium and Cyanide Removal
Based on the results from the above batch experiments, operating
parameters were determined for bench-scale continuous flow
experiments. In the continuous flow mode, liquid was introduced
into the reactor with a metering pump which discharged into the
bottom of the reactor. The reactor was adjusted so that about two
liters of sample were constantly present in the reactor during the
continuous flow experiments. The conditions used in a continuous
flow treatment were short residence time (about one hour) and a pH
of about 7.8. In addition, the amount of ferrous iron added, the
air sparge rate, and the rpm of the stirrer were the same as
employed in the batch runs. Both the biotreatment plant influent
and effluent samples were tested under these conditions. The
results are shown below in Table 12:
TABLE 12 ______________________________________ Effect of
Continuous Flow on Selenium Removal Biotreatment Plant Effluent,
Influent, Sampling Time (min.): Se, mg/l Se, mg/l
______________________________________ 0 2300 675 60 22 221
______________________________________
Table 12 shows that selenium can be effectively removed using a
continuous-flow treatment.
The following Table 13 shows that cyanide removal is equally
effective for both samples under continuous-flow conditions.
TABLE 13 ______________________________________ Effect of
Continuous Flow on Cyanide Removal Biotreatment Plant Effluent,
Influent, Sampling Time (min.): CN, mg/l CN, mg/l
______________________________________ 0 0.02 0.18 60 <0.01 0.01
______________________________________
Bioassay testing was performed on the treated waste water from the
continuous-flow treatments to determine the effects of the
treatment upon the level of residual biotoxicity.
Results from Bioassay 96-hr static fish kill tests showed that the
process of the present invention is capable of enhanced reduction
of biotoxicity over biotreatment alone (i.e., 100% survival in the
biotreatment plant effluent treated by the process of the present
invention versus 90% survival for the untreated biotreatment plant
effluent.)
Treatment of the biotreatment plant influent by the process of the
present invention alone achieved an LC of 45%, which, in terms of
Toxicity-Concentration represents over one third of the biotoxicity
reduction achieved by the biotreatment plant system. This is a
remarkable level of toxicity reduction given the relatively short
reactor residence times used with the process of the present
invention. Accordingly, placing the treatment process of the
present invention upstream of biotreatment augments biotoxicity
reduction as well as buffers the biotreatment system from peaks of
toxicants that might otherwise inhibit biological treatment.
EXAMPLE 15
A sample of a biotreatment plant influent (BI) and a sample of the
biotreatment plant effluent (BE) were taken and stored in a
refrigerated room (about 4.degree. C.) upon receipt. A bench scale
continuous treatment system was used to test about 12 liters each
of samples BI and BE by the method of the invention. The continuous
treatment system used the reaction vessel and stirrer employed in
Example 14 to test both samples. The pH of each sample was
initially adjusted to about 7.8. Sodium hydroxide (0.25 N) was
employed in both continuous treatments to help maintain the pH at
about 7.8. The total sodium hydroxide added during sample BI's
treatment was about 0.0024 eq/1 and the total amount of sodium
hydroxide added during sample BE's treatment was about 0.0020 eq/1.
About 0.042 gram of Colloidal 691 brand anti-foam was added to
sample BI, but no anti-foam was added to sample BE. The air sparge
rate used in treating sample BI was maintained at about 0.9l/min
(uncalibrated). However, the air sparge rate used in treating
sample BE was about 2l/min (uncalibrated) with slight foaming. The
stirrer was run at about 500 rpm for both samples and the reactor
residence time used in treating both samples was about 30 minutes.
Ferrous iron was metered in-line to each sample stream. A ferrous
iron dosage of 100 ppm was employed in treating sample BI and
sufficient ferrous iron was added to sample BE to raise sample BE's
ferrous iron content to about 100 ppm.
Nalco 8173 brand flocculant was used to flocculate samples BI and
BE. The flocculant was added at 6 ppm for each test. The
flocculations were each performed in a 2-liter graduated cylinder.
The solids generated from sample BE were allowed to settle out
overnight, and the solids generated from sample BI were allowed to
settle out for 3 nights prior to removing the solids by filtering
each sample through a Whatman #1 brand filter paper. Ten liters of
the supernatant obtained from each treated sample were separately
stored in plastic containers for the bioassay fish kill test, and
about 1 liter of the supernatant obtained from each treated sample
was stored in nalgene plastic bottles for the other tests. The
final pH of the supernatant obtained from samples BI and BE were
about 7.18 and about 7.57, respectively. The results obtained from
this experiment are sets forth in Table 14 below.
TABLE 14
__________________________________________________________________________
BI BI PERCENT BE BE PERCENT TEST UNITS RAW TREATED REMOVED RAW
TREATED REMOVED
__________________________________________________________________________
Al mg/l 0.18 0.04 77.8 0.24 0.06 75.0 Fe mg/l 0.71 0.25 64.8 0.77
0.28 63.6 Na mg/l 117 183 -56.4 121 169 -39.7 V mg/l 0.01 <0.004
>60.0 0.01 <0.004 >60.0 As (furnace) mg/l 2 <1 >50.0
3 1 66.7 Hg ug/l 1.3 1.6 -23.1 2.0 0.5 75.0 Se (furnace) mg/l 0.43
0.59 -37.2 0.44 <0.05 >88.6 pH 7.05 7.18 NA 6.92 7.57 NA TSS
mg/l 52 6 88.5 8 4 50.0 TDS mg/l 476 681 -43.1 472 598 -26.7
Cyanide mg/l 0.25 0.17 32.0 0.20 <0.04 >80.0 BOD mg/l 225 40
82.2 230 3 98.7 COD mg/l 542 244 55.0 318 42 86.8 TOC mg/l 227.5 63
72.3 74 19 74.3 Oil & Grease mg/l 50 <0.1 >99.8 30
<0.1 >99.7 Phenolics mg/l 16.4 1.1 93.3 9.63 0.01 99.9
Bioassay, 500 100,000 19,900 100% 100% -- Fish kill LC.sub.50 mg/l
mg/l
__________________________________________________________________________
(fish = Flathead minnows)
Table 14 shows that the process of the present invention is capable
of simultaneously achieving significant reductions in light metals
(e.g., aluminum), heavy metals (e.g., vanadium, mercury, arsenic,
selenium), cyanide, TSS, BOD, COD, TOC, oil and grease, as well as
phenolics.
In yet another version of the invention, volatile organics are
removed from the aqueous solution simultaneously with the removal
of any of the above discussed contaminants that may be present in
the solution. In general, the method of the present invention can
reduce the concentration in the aqueous solution of any volatile
organic having a Henry's Law constant of at least about 0.02. Since
substances having higher Henry's Law constants are more volatile,
and therefore usually easier to remove from a solution, it is
preferred that each volatile organic have a Henry's Law constant of
at least about 0.05, and more preferably at least about 0.25.
Exemplary volatile organics that can be treated by the instant
invention include, but are not necessarily limited to, benzene,
xylene, ethylbenzene, t-1,2-dichloroethene, trichloroethene,
tetrachloroethene, 1,1,1-trichloroethene, 1,1-dichloroethene, vinyl
chloride, 1,2-dichlorobenzene, and 1,4-dichlorobenzene.
Typically, the oxidant gas employed to oxidize the ferrous ions
serves a dual function in that it (a) oxidizes the ferrous ions and
(b) acts as a gaseous phase. Accordingly, the volatile organics are
partitioned between the gaseous phase and a liquid phase comprising
the aqueous solution.
Usually, the gas is introduced proximate the bottom of a treatment
vessel at a rate sufficient to achieve an average volumetric flux
ratio of gas to water of at least about 20, i.e., on an average at
least about 20 unit volumes of gas cross a unit area of a given
surface in a specified time interval for each unit volume of water
that crosses the same unit area of the surface in the same time
interval. It is preferred to use a higher average volumetric flux
ratio because the higher the average flux ratio, the faster the
removal of the volatile organic from the aqueous solution, all
other factors being constant. However, economics dictates a maximum
average volumetric flux ratio of about 100. Preferably, the average
volumetric flux ratio is about 30 to about 90, and more preferably
about 40 to about 80.
One of the major advantages resulting from the present invention's
ability to simultaneously remove volatile organic contaminants and
non-volatile contaminants is that the same reaction vessel
accomplishes both results. This eliminates additional capital
costs. In addition, the vessel need not, and preferably does not,
contain any packing material conventionally used in volatile
organic removal equipment. By avoiding the use of packing material,
the present invention is effective for removing volatile organics
without exhibiting the typical decrease in efficiency common to
packed towers. The decrease in efficiency is due to the build-up of
substances on the packing material and necessitates the periodic
cleaning or replacement of the packing material.
The vessel preferably employed in the present invention to
simultaneously remove volatile organic and non-volatile
contaminants has an internal diameter to internal height ratio much
greater than that of vessels conventionally used to remove volatile
organics. Typically, the vessel employed in the present invention
has an internal diameter to internal height ratio of about 1:1 to
about 1:4, preferably about 1:1.1 to about 1:3, and more preferably
about 1:1.2 to about 1:2. For example, very desirable vessels have
internal diameter to internal height ratios of about 6 feet to
about 9 feet, about 8 feet to about 12 feet, and about 11 feet to
about 15 feet. In addition, the impeller of the mixer employed to
shear the gas bubbles generally has a diameter of about 30 to about
40 percent of the internal diameter of the vessel, and the sparger
employed to distribute the bubbles generally has a diameter about
75 to about 85 percent of the diameter of the impeller.
The removal of volatile organics from the aqueous solution can be
performed either by a batch or a continuous process. In the batch
process, the solution is generally sparged with the oxidant gas for
a least about 15 minutes. In the continuous process, the average
residence time that the solution is sparged with the oxidant gas is
also about 15 minutes. The maximum sparge or treatment time for
both methods is also dictated by economics and is generally about 2
hours. Preferably, the treatment time is about 0.5 to about 1.5
hours.
Another parameter affecting the volatile organic removal efficacy
of the process of the present invention is the pH of the aqueous
solution being treated. Preferably, the pH of the aqueous solution
is maintained with a range of about 6 to about 9.5, more preferably
within a range of about 6.5 to about 9, and optimally within a
range of about 7.5 to about 8. The pH can be maintained within
these ranges with a base, such as one selected from the group
consisting of ammonia, hydroxide containing bases, and mixtures
thereof. When necessary, the pH can be maintained within these
ranges with an acid.
The size of the bubbles being sparged or introduced into the
aqueous solution can also affect the ability of the present
invention to remove volatile organics from aqueous solutions. In
general, the smaller the bubble size the more surface area
available for mass transfer of the volatile organics between the
liquid and gas phases. Accordingly, it is preferred to reduce the
average bubble diameter by strongly agitating the solution.
Typically, the process of the present invention reduces the
concentration of each volatile organic present (as well as the
total volatile organics) in an aqueous solution by at least about
80 percent. Depending on the type of volatile organic being
removed, the treatment time, the average volumetric flux ratio of
gas to water, the pH of the aqueous solution being treated, and the
volatile organic mass transfer rate between the liquid and gas
phases, the process of the instant invention is capable of removing
more than about 90 percent, preferably more than about 95 percent,
and even substantially all of the volatile organics initially
present in the aqueous solution.
The volatile organic removal efficiency in present invention the
can also be increased by repeatedly treating an aqueous solution.
For example, the effluent from a first treatment stage can be
subjected to a similar treatment to obtain comparable further
reductions of any volatile organic and/or other above described
contaminant.
The following examples illustrate embodiments of the invention
wherein volatile organics and other contaminants are simultaneously
removed from an aqueous solution.
EXAMPLE 16
A sample of waste water combined from different sources was
characterized for heavy metals and inorganic and organic compounds
using the analytical methods listed in Table 15.
TABLE 15 ______________________________________ Test Methods Test
Analytical Method ______________________________________ Heavy
Metals Copper ICP Lead ICP Iron ICP Mercury GFAA Selenium HGAA
Inorganic Components Cyanide Distillation/ Colorimetry Phenolics
E-402.1 Organic Components Benzene E-8020/5030 Toluene E-8020/5030
Xylene E-8020/5030 Ethylbenzene E-8020/5030
______________________________________
A summary of the raw waste water characteristics is given in Table
16.
TABLE 16 ______________________________________ Benzene, mg/l 17.9
Toluene, mg/l 41.9 Xylenes, mg/l 32.6 Ethylbenzene, mg/l 5.57 1,3
Dichlorobenzene, mg/l 7.65 1,4 Dichlorobenzene, mg/l 3.1 1,2
Dichlorobenzene, mg/l 2.3 Chlorobenzene, mg/l <2.5 Iron, mg/l
47.8 Copper, mg/l 0.15 Lead, mg/l 0.77 Selenium, ug/l 3 Mercury,
ug/l <1 Cyanide, mg/l 0.05 Oil & Grease, mg/l 9.1 Phenolics,
mg/l 21 ______________________________________
The reactor vessel and stirrer used to evaluate waste water
treatability were the same as employed in Examples 14 and 15. All
treatments were carried out on a batch basis under steady state
conditions with respect to temperature, air-flow rate, and turbine
speed. Samples were taken with a syringe, flocculated with 0.5 ml
of 0.3 g/l Nalco 8173 brand flocculent, filtered, and transferred
to a 40 ml volatile organic analysis (VOA) vial.
Analyses for benzene, toluene, xylene, and ethylbenzene (BTXE) were
done by liquid chromatography and metals analyses were done by
emission spectroscopy.
Simultaneous Treatment
Enough caustic was added to the slightly acidic sample to bring its
pH up to about 7.7. Although analysis of the raw sample indicated
that the sample contained a considerable amount of iron, ferrous
iron (100 ppm) was added. Treatment began with the initiation of
air flow (about 2.8 l/min) and continued for a period of about 80
minutes. Treatment results are given in Table 17.
TABLE 17
__________________________________________________________________________
Simultaneous Treatment (Metals and VOC)
__________________________________________________________________________
Results: VOC (as BTXE) Ethyl Time, Benzene % Toluene % Xylene %
benzene % Min. mg/l Reduction mg/l Reduction mg/l Reduction mg/l
Reduction
__________________________________________________________________________
0 11 -- 13 -- 8.1 -- 5.6 -- 6 2.9 73.6 3.8 70.1 1.8 77.8 0.63 88.8
12 0.79 92.8 0.92 92.9 0.57 93.0 0.15 97.3 18 0.29 97.4 0.21 98.4
0.086 98.9 0.041 99.3 24 0.22 98.0 0.065 99.5 0.086 98.9 0.010 99.8
30 0.19 98.3 0.027 99.8 0.043 99.5 0.010 99.8
__________________________________________________________________________
Results: Metals Time, Copper, % Lead % Iron % Min. mg/l Reduction
mg/l Reduction mg/l Reduction
__________________________________________________________________________
0 0.15 -- 0.77 -- 147.8 -- 7 <0.03 80.0 <0.04 94.8 17.8 88.0
13 <0.03 80.0 <0.04 94.8 0.3 99.8 25 <0.03 80.0 <0.04
94.8 1.1 99.3 31 0.04 73.3 <0.04 94.8 0.6 99.6
__________________________________________________________________________
Sequential Treatment
Treatment was carried out as described above for simultaneous
treatment with the exception that the ferrous iron was added after
air stripping for about 60 minutes. Treatment results are given in
Table 18.
TABLE 18
__________________________________________________________________________
Sequential Treatment (Metals and VOC)
__________________________________________________________________________
Results: VOC (as BTXE) Ethyl Time, Benzene % Toluene % Xylene %
benzene % Min. mg/l Reduction mg/l Reduction mg/l Reduction mg/l
Reduction
__________________________________________________________________________
0 8.3 -- 14.2 -- 4.4 -- 2.8 -- 10 0.87 89.5 1.3 90.8 1.2 72.7 0.3
89.3 20 0.22 97.3 0.092 99.4 0.15 96.6 0.040 98.6 60 0.14 98.3
0.023 99.8 0.050 98.9 0.015 99.5 90 0.11 98.7 0.012 99.9 0.014 99.7
0.010 99.6 120 0.06 99.3 0.011 99.9 0.011 99.8 0.006 99.8
__________________________________________________________________________
Results: Metals Time, Copper, % Lead % Iron % Min. mg/l Reduction
mg/l Reduction mg/l Reduction
__________________________________________________________________________
0 0.15 -- 0.77 -- 47.8 -- 30 <0.03 80.0 <0.04 94.8 1.2 97.5
60 <0.03 80.0 <0.04 94.8 1.6* 96.7 70 0.07 53.3 <0.04 94.8
0.3 99.7
__________________________________________________________________________
*Measured prior to the addition of 100 ppm soluble iron, i.e.,
after taking an aliquot of the treated sample 60 minutes into the
run, 100 ppm of ferrous iron were added to raise the iron content
of the the sample to about 101.6 ppm.
The data set forth in Tables 17 and 18 indicate that simultaneous
and sequential treatments yield comparable results. In addition,
the fact that (a) the composite sample contained a relatively large
amount of iron and (b) the metals treatment took place within the
initial 60-minute period indicates that metal encapsulation and VOC
stripping are occurring simultaneously, even when additional
ferrous iron is added sequentially. Since a substantial reduction
in the metals content was obtained prior to the addition of ferrous
iron (see Table 18), the waste iron found in the raw sample is
suitable as a ferrous iron source for use in the treatment process
of the instant invention.
The data set forth in Tables 17 and 18 also indicate that an
aqueous sample can be treated first to remove the volatile organics
and then to remove the non-volatile organic contaminants or can be
treated to simultaneously remove both the volatile organic and
non-volatile organic contaminants. Accordingly, in a further
embodiment of the present invention an aqueous solution is treated
to remove its volatile organic contents irrespective of whether any
non-volatile contaminants are also simultaneously removed.
The parameters discussed above with respect to simultaneously
removing volatile organic and non-volatile organic contaminants,
i.e., the treatment time, the average volumetric flux ratio of gas
to water, the pH of the aqueous solution being treated, and the
average size of the gas bubbles, are equally applicable when the
only contaminant of concern are volatile organics. In addition, the
above discussed reactor vessel is also preferably employed to
remove volatile organics. However, since there is no need to
oxidize any ferrous ions, the gas employed to remove volatile
organics need not be limited to oxidizing gases. A commercially
available non-oxidizing gas that can be used in this version of the
invention is nitrogen. Nevertheless, since air is the cheapest
available gas, air is still the gas of choice.
In the following example, a solution is treated to reduce its
volatile organic content.
EXAMPLE 17
The system used to evaluate diffused air stripping were the same as
employed in Examples 14-16. Two samples were treated in a batch
mode. In the batch mode test, the air flow control valve was
adjusted to give the desired flow and then the main shutoff valve
was closed. The reactor was filled with a predetermined amount of
liquid. The turbine was adjusted to a rotation speed of about 500
rpm. An initial sample was taken with the timer started when the
gas shutoff valve was opened. Gas flow rate, temperature, and
turbine speed were monitored throughout the run. Samples were taken
with a syringe and transferred to a 40 ml VOA vial. The parameters
used in each batch mode run are set forth in Table 19.
One sample was treated in a continuous mode. In the continuous
mode, liquid was pumped into the reactor via a tube that opened at
the bottom of the reactor and exited from an overflow port on the
side of the reactor. The reactor was filled with liquid and air
stripping was run on a volume (air) to volume (liquid) ratio basis
using previous batch test results to estimate the proper ratio. The
objective was to get close to steady state conditions. After the
liquid metering pump was started and the system operated for at
least three volume changes, the inlet and outlet liquid flows were
sampled and analyzed. The parameters used in the continuous mode
run are also set forth in the following Table 19.
TABLE 19 ______________________________________ Experimental
Conditions Run Number Continuous Batch Mode Mode 1 2 3
______________________________________ Reactor volume - liter 2 2 2
Air flow rate - 1 min.sup.-1 1.0 2.0 1.2 Water flow rate - ml
min.sup.-1 -- -- 15 Temperature - .degree.C. 10 10 10 Mixer - RPM
500 500 500 ______________________________________
The 40 ml VOA samples were analyzed by EPA methods 601 and 602. The
results are set forth in Tables 20-22.
TABLE 20
__________________________________________________________________________
Run 1
__________________________________________________________________________
Time, minutes 15 30 45 Volatile 0 % % % Organics (ug/l) (ug/l)
Reduction (ug/l) Reduction (ug/l) Reduction
__________________________________________________________________________
Toluene 410 150 36.6 52 87.3 19 95.4 Benzene 12 3.9 67.5 1.5 87.5
0.7 94.2 Xylenes 180 60 66.7 25 86.1 10 94.4 Ethyl- 32 8.8 72.5 2.7
91.6 0.9 97.2 benzene t-1, 2- 6.3 1.0 84.1 ND.sup.1 100 ND 100
dichloro- ethene tri- 7300 1500 79.5 480 93.4 148 98.0 chloro-
ethene tetra- 2300 450 80.4 55 97.6 9.1 99.6 chloro- ethene 1,1,1-
3.2 ND 100 ND 100 ND 100 tri- chloro- ethene 1,1- 5.8 ND 100 ND 100
ND 100 dichloro- ethene vinyl 32 ND 100 ND 100 ND 100 chloride 1,2-
110 83 24.5 73 33.6 48 56.4 dichloro- benzene 1,4- 19 12 36.8 5.1
73.2 5.2 72.6 dichloro- benzene
__________________________________________________________________________
Time, minutes 60 75 90 Volatile % % % Organics (ug/l) Reduction
(ug/l) Reduction (ug/l) Reduction
__________________________________________________________________________
Toluene 10 97.6 3.1 99.2 1.8 99.6 Benzene 0.7 94.2 ND 100 0.6 95.0
Xylenes 3 98.3 0.9 99.5 1.0 99.4 Ethyl- ND 100 ND 100 ND 100
benzene t-1, 2- ND 100 ND 100 ND 100 dichloro- ethene tri- 25 99.7
18 99.8 11 99.8 chloro- ethene tetra- 2.5 99.9 2.3 99.9 1.7 99.9
chloro- ethene 1,1,1- ND 100 ND 100 ND 100 tri- chloro- ethene 1,1-
ND 100 ND 100 ND 100 dichloro- ethene vinyl ND 100 ND 100 ND 100
chloride 1,2- 41 62.7 36 67.2 12 89.1 dichloro- benzene 1,4- 2 89.5
1.2 93.7 1.3 93.2 dichloro- benzene
__________________________________________________________________________
.sup.1 ND denotes none detected.
TABLE 21
__________________________________________________________________________
Run 2
__________________________________________________________________________
Time, minutes 15 30 45 Volatile 0 % % % Organics (ug/l) (ug/l)
Reduction (ug/l) Reduction (ug/l) Reduction
__________________________________________________________________________
Toluene 84,000 61,000 27.4 28,000 66.7 19,000 77.4 Benzene 150 47
68.7 13 91.3 ND 100 Xylenes 15,000 11,000 26.7 8,300 44.7 6,000
60.0 Ethyl- 2,300 1,500 34.8 990 57.0 580 74.8 benzene tri- 1,700
490 71.2 100 94.1 26 98.5 chloro- ethene tetra- 7,900 3,900 50.6
1,800 77.2 790 90.0 chloro- ethene 1,1,1- 3,800 540 85.8 47 98.8
4.6 99.9 tri- chloro- ethene 1,1- 11 2.9 73.6 0.6 94.5 ND 100
dichloro- ethene vinyl 16 ND 100 ND 100 ND 100 chloride 1,2- 2,300
2,100 8.7 2,500 -8.7 2,700 -17.4 dichloro- benzene 1,4- 380 300
21.1 391 -2.9 690 -81.6 dichloro- benzene
__________________________________________________________________________
Time, minutes 60 75 90 Volatile % % % Organics (ug/l) Reduction
(ug/l) Reduction (ug/l) Reduction
__________________________________________________________________________
Toluene 8,700 89.6 790 99.1 1.0 100 Benzene ND 100 ND 100 ND 100
Xylenes 4,000 73.3 1,900 87.3 760 94.9 Ethyl- 344 85.0 130 94.3 44
98.1 benzene tri- ND 100 ND 100 ND 100 chloro- ethene tetra- 330
95.8 72 99.1 10 99.9 chloro- ethene 1,1,1- 1.1 100 ND 100 0.7 100
tri- chloro- ethene 1,1- ND 100 ND 100 ND 100 dichloro- ethene
vinyl ND 100 ND 100 ND 100 chloride 1,2- 2,600 -13.0 2,100 8.7
1,900 17.4 dichloro- benzene 1,4- 710 -86.8 260 31.6 200 47.4
dichloro- benzene
__________________________________________________________________________
TABLE 22
__________________________________________________________________________
Run 3 Reactor 1 Reactor 2 Overall Volatile In Out % In Out % %
Organics (ug/l) (ug/l) Reduction (ug/l) (ug/l) Reduction Reduction
__________________________________________________________________________
Toluene 32,000 9,500 70.3 9,200 1,100 88.0 96.6 Benzene 28 2.9 89.6
1.8 ND 100 100 Xylenes 10,000 1,000 90.0 880 59 93.3 99.4 Ethyl-
1,900 140 92.6 110 8.7 92.1 99.5 benzene tri- 1,500 60 96.0 45 3.5
92.2 99.8 chloro- ethene tetra- 4,400 180 95.9 134 7.9 94.1 99.8
chloro- ethene 1,1,1- 1,400 35 97.5 27 1.1 95.9 99.9 tri- chloro-
ethene 1,1- 12 3.2 73.3 ND ND -- -- dichloro- ethene vinyl 18 ND
100 ND ND 100 100 chloride 1,2- 2,600 560 78.5 540 87 83.9 96.7
dichloro- benzene 1,4- 610 170 72.1 150 12 92.0 98.0 dichloro-
benzene
__________________________________________________________________________
The data set forth in Tables 20 to 22 indicate that excellent
reductions in volatile organic concentrations are obtainable by the
process of the present invention.
Other aspects of this invention are described in U.S. Pat.
applications Ser. No. 477,212, filed Mar. 21, 1983, now abandoned,
and U.S. Pat. Ser. No. 042,565, filed Apr. 16, 1987, as well as
European patent application 84901534.2, filed Nov. 20, 1984, these
documents being incorporated herein by reference.
Although the present invention has been described in considerable
detail with reference to certain preferred versions thereof, other
versions are possible. For example, the reactor vessel, although
described as having an average diameter to height length ratio, can
have a cross-sectional area shape that is polygonal as well as
circular. In addition, the volatile organic removal embodiment of
the present invention can be employed with prior art processes
adapted to remove non-volatile contaminants, e.g., the mercury and
sulfide precipitation processes. In general, an aqueous solution is
treated by the prior art process with the simultaneous introduction
of a gas into the aqueous solution as taught herein. Furthermore,
the processes of the present invention can be use to treat
effluents from prior art waste water treatment processes.
Therefore, the spirit and scope of the appended claims should not
necessarily be limited to the description of the preferred versions
contained herein.
* * * * *